Paint Gallon Estimator for Multi-Room Floorplans: The Complete Guide to Buying the Right Amount of Paint

The Paint Gallon Estimator for Multi-Room Floorplans is a free online tool that calculates exactly how many gallons of paint you need for an entire home or multi-room project in one pass. Instead of juggling a notepad, a calculator, and a fistful of room measurements, you enter each room’s dimensions, door and window counts, number of coats, and finish type — and the tool instantly returns total paintable surface area, gallons required, and an estimated project cost, complete with a scaled floorplan diagram.

People reach for this estimator because paint is sold by the gallon, and getting the math wrong is expensive in both directions. Buy too little and you make a second trip to the store, risking a slightly different dye lot that shows up as a visible stripe on your wall. Buy too much and you have wasted money on paint you will never use. A reliable estimate closes that gap, especially across five, ten, or twenty rooms where small per-room errors compound into a large total.

Who should use it? Homeowners repainting a single floor, landlords refreshing units between tenants, professional painters quoting jobs, interior designers sourcing materials, property managers budgeting for renovations, and DIYers tackling their first whole-home project. If you have ever stood in the paint aisle wondering, “How many gallons do I need for a 12×14 living room plus two bedrooms?” — this calculator is built for you.

The benefits show up in real money and real time. A homeowner painting a 2,000-square-foot house can save $60–$120 by avoiding overbuying. A contractor quoting six rooms can produce a defensible material estimate in under two minutes instead of sketching numbers on the back of an invoice. Real-life applications range from a first-apartment refresh to a full rental-turnover repaint, a flip-and-sell renovation, or a commercial office repainting contract. To round out a renovation budget, you might pair this paint estimate with our Square Footage Calculator for flooring quantities or our BTU Calculator for sizing heating and cooling in the same rooms.

What Is the Paint Gallon Estimator for Multi-Room Floorplans?

Definition

A paint gallon estimator is a digital calculator that converts room geometry — length, width, height, and openings — into a paint purchase quantity measured in gallons. The “multi-room floorplan” version goes one step further: it accepts an unlimited list of rooms, calculates each one independently, and rolls the results into a single project total.

Purpose

The purpose is to replace rough mental math with a transparent, repeatable calculation. Most people guess paint quantities using rules of thumb like “one gallon per room,” which works for small bedrooms but fails badly on open-concept living areas, vaulted ceilings, or rooms with many windows. This tool replaces guessing with geometry.

Background

Paint coverage calculators have existed for decades, first as paper slide-rule wheels sold by paint manufacturers, then as simple single-room web forms. The multi-room variant is newer, driven by the rise of whole-home DIY projects and professional painters who quote several rooms per quote. Modern versions add finish-type multipliers, primer options, waste buffers, and visual floorplan diagrams.

Importance

Accurate paint estimation matters because paint is a consumable with a strict return profile. Most retailers do not accept returns on mixed paint, so every unused gallon is a sunk cost. Equally, an underestimate that forces a mid-project store run risks color mismatch. Getting the number right the first time protects both your budget and your finish quality.

How This Calculator Works

The estimator follows a five-stage pipeline, repeated for every room and then aggregated.

Stage 1 — Collect Inputs

For each room you enter:

• Room name (for the report)
• Length and width (in feet)
• Wall height (in feet)
• Number of doors
• Number of windows
• Number of coats

At the project level you set:

• Coverage rate (square feet per gallon, default 400)
• Price per gallon
• Door area (default 21 ft²)
• Window area (default 16 ft²)
• Finish type (flat, eggshell, satin, semi-gloss, gloss)
• Wall condition (smooth, textured, primed)
• Toggles for ceiling paint, primer coat, rounding, and a 10% waste buffer

Stage 2 — Compute Wall Area

The tool calculates the gross wall area by multiplying the room’s perimeter by its height, then subtracts the area taken up by doors and windows.

Stage 3 — Apply Coats and Options

It multiplies the net wall area (plus optional ceiling) by the number of coats, adds a primer coat if requested, and applies finish and condition multipliers to the coverage rate.

Stage 4 — Convert to Gallons

The adjusted paintable area is divided by the effective coverage rate, and a waste buffer is applied if enabled.

Stage 5 — Aggregate and Visualize

Per-room gallons and costs are summed into a project total, displayed in a hero number, a bar chart, a breakdown table, and a scaled floorplan diagram.

Variables and Units

Formula Explained

The calculator relies on a core geometry formula plus a coverage conversion. Here is the exact math.

The Core Formula

Variable Explanation

• 2 × (L + W) is the perimeter of a rectangular room, in feet.
• × H converts perimeter to wall surface area in square feet.
• D × A_d subtracts door openings (21 ft² per standard interior door).
• N × A_w subtracts window openings (16 ft² per standard window).
• × C scales the area by the number of coats.
• R is the manufacturer-stated coverage, typically 350–400 ft² per gallon.
• Waste Factor is 1.10 when a 10% buffer is applied, 1.00 otherwise.

Units

All lengths are in feet. Areas are in square feet (ft²). Volume of paint is in U.S. gallons. One gallon covers roughly 350–400 square feet of smooth wall with a single coat of standard interior latex.

Example Calculation

Consider a 14 × 12 living room with 9-foot walls, 2 doors, 3 windows, and 2 coats, using satin paint at $45 per gallon.

1. Perimeter = 2 × (14 + 12) = 52 ft
2. Gross wall area = 52 × 9 = 468 ft²
3. Openings = (2 × 21) + (3 × 16) = 42 + 48 = 90 ft²
4. Net wall area = 468 − 90 = 378 ft²
5. Paintable area = 378 × 2 coats = 756 ft²
6. Coverage at 400 ft²/gal, satin multiplier 0.95 → effective 380 ft²/gal
7. Gallons (no waste) = 756 ÷ 380 = 1.99 → 2 gallons
8. With 10% waste buffer = 756 × 1.10 ÷ 380 = 2.19 → 3 gallons (rounded up)
9. Cost = 3 × $45 = $135

 

💡 Pro tip: Always round up to whole gallons. Paint is sold by the gallon, and a fraction of a gallon still costs a full gallon — but you cannot buy a “partial gallon” to finish a job.

Common Mistakes

• Forgetting to subtract openings — counting doors and windows as paintable area inflates the estimate by 15–25%.
• Using perimeter × width instead of perimeter × height — a common slip that produces wildly wrong numbers.
• Applying one coat to the area, not the coats multiplier — forgetting the coats factor doubles your underestimate.
• Using 400 ft²/gal for textured walls — textured surfaces reduce effective coverage to about 300–340 ft²/gal.
• Ignoring finish type — gloss and semi-gloss cover slightly less than flat due to lower pigment volume.

How to Use the Calculator

Follow these steps for an accurate whole-home estimate.

1. Set your project settings first. Enter your coverage rate (check the paint can label — most interior latex is 350–400 ft²/gal), price per gallon, and confirm the default door (21 ft²) and window (16 ft²) areas match your openings.
2. Choose a finish type. Select flat, eggshell, satin, semi-gloss, or gloss from the dropdown. Higher sheen slightly reduces coverage.
3. Pick a wall condition. Smooth walls use the base rate; textured walls reduce coverage; previously primed walls gain a small boost.
4. Add a room. Click “Add Room” and give it a name like “Living Room.”
5. Enter length, width, and wall height in feet. Use decimals for partial feet (e.g., 12.5).
6. Count doors and windows. Enter the number of each — the calculator subtracts their standard areas automatically.
7. Set the number of coats. Use 2 for most color refreshes, 3 for dark-over-light transitions.
8. Toggle ceiling, primer, rounding, and waste as needed. Most users enable rounding and the 10% waste buffer.
9. Repeat for every room. The bar chart, breakdown table, and floorplan diagram update live as you type.
10. Read the hero result. The large number is your total gallons; the cost figure is your material budget.
11. Print or save the report using the Print button for a PDF to take to the store or attach to a quote.

 

⚠️ Tip: If you have vaulted or cathedral ceilings, break the wall into segments. Measure the shorter wall sections separately and add them as additional “rooms” with the correct heights.

Example Calculations

Beginner Example — Single Bedroom

• Perimeter = 2 × (12 + 10) = 44 ft
• Gross wall area = 44 × 8 = 352 ft²
• Openings = (1 × 21) + (2 × 16) = 53 ft²
• Net wall area = 299 ft²
• Paintable area = 299 × 2 = 598 ft²
• Gallons = 598 ÷ 400 = 1.50 → 2 gallons (rounded, no waste)
• With 10% waste → 1.65 → 2 gallons
• Cost = 2 × $42 = $84

Intermediate Example — Three-Room Apartment

Running each through the estimator at 400 ft²/gal, satin finish, with a 10% waste buffer:

Advanced Example — Whole-Home with Primer, Ceiling, and Textured Walls

A 2,000 ft² home with 8 rooms, vaulted great room, smooth walls except the great room (lightly textured), primer requested throughout, ceilings included, semi-gloss trim counted as separate “rooms.” After entering all eight rooms with the primer toggle on and ceiling toggle on, the estimator might output:

• Total paintable area: ~5,400 ft²
• Effective coverage (semi-gloss, mixed smooth/textured): ~370 ft²/gal
• Gallons with 10% waste: ~16 gallons
• Cost @ $52/gal premium paint: $832

This kind of multi-room, multi-condition estimate is exactly where a calculator earns its keep — manual math would take 20 minutes and likely contain an error.

Benefits

1. Saves money by preventing overbuying. Unused mixed paint is rarely returnable; an accurate estimate keeps those dollars in your pocket.
2. Prevents color-mismatch store runs. Buying all paint at once guarantees a single dye lot and consistent color across every wall.
3. Handles unlimited rooms. No need to run eight separate calculations and add them by hand.
4. Accounts for doors and windows automatically. No more wondering whether to subtract 21 or 16 square feet per opening.
5. Adjusts for finish type. Gloss, semi-gloss, and satin are properly penalized for lower coverage.
6. Adjusts for wall texture. Textured and heavily textured walls reduce coverage realistically.
7. Includes a primer option. Transitions from dark to light colors get the extra coat they need.
8. Adds a waste buffer. The 10% toggle covers spills, touch-ups, and roller waste.
9. Produces a cost estimate. Multiply gallons by your per-gallon price for an instant budget.
10. Visualizes the floorplan. The scaled diagram helps you sanity-check room proportions and paint share.
11. Enables transparent quoting. Contractors can show clients the breakdown table as proof of a fair material estimate.
12. Works on any device. Mobile-friendly for on-site measurements at a property.
13. Free and private. All math runs in your browser — no sign-up, no data upload.

Features

• Multi-room input with add, duplicate, and remove buttons per room.
• Live calculation — no “calculate” button; numbers update on every keystroke.
• Finish and condition dropdowns that adjust effective coverage in real time.
• Ceiling paint toggle for full-room repainting.
• Primer coat toggle for color transitions.
• Round-up toggle to enforce whole-gallon purchasing.
• 10% waste buffer toggle for spills and touch-ups.
• Per-room stat cards showing net wall area, paintable area, and gallons.
• Hero result panel with total gallons, project cost, paintable area, room count, and average coats.
• Floorplan SVG diagram scaled by footprint, color-coded by paint share.
• Horizontal bar chart of paint distribution per room.
• Detailed breakdown table with per-room and total rows.
• Buying recommendation with gallons-plus-quarts alternative and budget estimate.
• Print-to-PDF report for store trips or client quotes.
• Transparent, light-green theme that blends into any WordPress site.

Applications

Construction and Home Improvement

Builders and renovators use the estimator during the finishing phase to order paint for new construction or remodels. Pairing it with our Concrete Calculator for foundations and our Roofing Calculator for the roof gives a full exterior-to-interior material picture. For lumber-based trim and shelving, the Board Foot Calculator handles the wood side.

Professional Painting Contractors

Painters use the breakdown table to quote material costs line-by-line. The per-room transparency builds trust with clients and speeds up approvals. Contractors tracking profitability can feed the material total into our Return on Investment (ROI) Calculator to verify margin.

Real Estate and Property Management

Landlords refreshing units between tenants estimate paint for entire apartments in one session. Investors evaluating a flip can pair the paint budget with the Rental Property Calculator to model total rehab costs against projected rental income.

Interior Design and Staging

Designers source paint for staged homes and model units. The scaled floorplan diagram helps visualize which rooms dominate the paint budget so designers can rebalance finish choices.

DIY and Everyday Home Projects

Homeowners tackling a first repaint, a nursery, or a rental refresh use the estimator to buy exactly what they need. For related landscaping touches around the exterior, the Mulch Calculator handles garden beds, and the Acreage Calculator covers larger lot measurements. If you are budgeting a larger renovation, the Home Equity Loan Calculator can show borrowing power for the project.

Education

Vocational and trade-school instructors use the tool to teach surface-area geometry and material estimation, showing students the formula and the live result side by side.

Advantages

• Speed. A ten-room estimate that takes 20 minutes by hand finishes in under two minutes.
• Accuracy. The geometry formula is exact; only the coverage rate carries real-world variability.
• Transparency. Every number is traceable through the breakdown table.
• Flexibility. Adjust coverage, finish, condition, primer, ceiling, and waste independently.
• Portability. Works on phones, tablets, and desktops with no install.
• Cost awareness. Instant budget figure prevents sticker shock at checkout.
• Visual sanity check. The floorplan diagram catches dimension entry errors at a glance.

Limitations

• Coverage varies by brand and batch. The 350–400 ft²/gal range is an average; premium paints may cover more, bargain paints less. Always check the can label.
• Standard opening sizes only. The 21 ft² door and 16 ft² window defaults fit standard interior openings. Oversized entry doors, sliding glass doors, and bay windows need custom areas.
• Rectangular rooms assumed. Rooms with angled walls, curves, or alcoves need to be broken into rectangular segments.
• No trim, baseboard, or door paint. The estimator covers walls (and optionally ceilings). Trim and door paint should be calculated separately using the door area as a guide.
• No labor estimate. The cost figure is materials only. Labor typically doubles or triples the material cost for a professional job.
• No exterior paint. Exterior surfaces, stucco, and masonry have very different coverage rates.
• Spray application differs. Airless sprayers use 25–30% more paint than rollers due to overspray.
• High-pigment colors. Deep reds, yellows, and some blues may require a tinted primer and three or more coats, which the tool handles via the coats and primer toggles but cannot fully predict.

Tips for Accurate Results

• Measure walls at the longest dimension. For rooms with bump-outs, use the outer wall length to avoid underestimating.
• Count a sliding glass door as two standard doors (about 42 ft²) or set a custom window area.
• Check the coverage rate on the paint can before trusting the 400 default. Some premium paints cover 450 ft²/gal; some economy paints cover only 300.
• Use 3 coats for dark-on-light transitions. A deep navy over white almost always needs three coats or a tinted primer.
• Enable the waste buffer for textured walls. Textured surfaces absorb more paint and create more roller waste.
• Separate ceiling paint from wall paint. Ceilings usually use flat white; walls use a different sheen and color. Toggle ceiling paint only if using the same product.
• Round up, always. Fractional gallons round up to whole gallons because paint is sold that way.
• Verify with a test patch. Paint a 4×4 ft section first to confirm coverage before buying the full quantity.
• Buy from one batch. Purchase all gallons at once and note the batch number for consistent color.

Common Mistakes

• Forgetting to subtract doors and windows — inflates the estimate by 15–25%.
• Using wall height as width — a slip that produces nonsensical numbers.
• Counting the ceiling as a wall without toggling the ceiling option — double-counts or omits it entirely.
• Using one coat when two are needed — the most common underestimate, especially over a darker existing color.
• Mixing metric and imperial units — all inputs should be in feet; mixing meters in will break the result.
• Ignoring finish type — gloss and semi-gloss cover less than flat, by roughly 5–10%.
• Buying exact gallons with no buffer — a small spill or touch-up can leave you a quart short with no matching paint.
• Forgetting primer for color transitions — going from dark to light without primer often requires an extra coat of finish paint anyway.
• Not rounding up — 2.6 gallons is not “about 2.5”; you must buy 3.

Frequently Asked Questions

1. How many square feet does one gallon of paint cover?

One gallon of standard interior latex paint covers approximately 350 to 400 square feet with a single coat on smooth walls. Premium paints may cover up to 450 ft², while economy paints can drop to 300 ft². Textured walls reduce coverage by 10–20%, and higher-sheen finishes (semi-gloss, gloss) cover slightly less than flat. Always check the coverage figure printed on the paint can before ordering.

2. How do I calculate paint for multiple rooms?

Measure each room’s length, width, and wall height, count doors and windows, and decide on the number of coats. Enter each room into the estimator — it calculates the net wall area per room, multiplies by coats, sums all rooms, and divides by the coverage rate to produce total gallons. The multi-room calculator automates what would otherwise be eight separate calculations added by hand.

3. What is the standard size of a door and window for paint estimates?

A standard interior door is about 21 square feet (typically 3 × 7 ft), and a standard window is about 16 square feet. The calculator subtracts these areas from the gross wall area. If you have oversized entry doors, sliding glass doors, or large picture windows, adjust the door and window area fields in the settings to match your actual openings.

4. How much extra paint should I buy for waste?

Industry guidance is to add 10% extra for spills, roller waste, touch-ups, and color matching. The calculator’s waste buffer toggle applies a 1.10 multiplier automatically. For textured walls or spray application, consider 15%. For very small rooms where a single quart could finish the job, the buffer may be unnecessary, but for most projects 10% is the safe default.

5. Do I need to paint the ceiling?

Ceilings are optional in this estimator. Toggle “Include ceiling” if you are painting the ceiling with the same paint. Most ceilings use a flat white paint, which is different from the wall paint, so many users leave the ceiling off and buy ceiling paint separately using the room’s length × width as the area.

6. How many coats of paint do I need?

Two coats is the standard for most interior repaints, delivering full color depth and even coverage. Use three coats when painting a dark color over a light one, a light color over a dark one, or when using deep, high-pigment colors like red or navy. A tinted primer can often replace the third coat and is toggled separately in the estimator.

7. What is the difference between flat, eggshell, satin, semi-gloss, and gloss paint?

These are finish sheens, ordered from least to most shiny. Flat hides imperfections but is less washable. Eggshell and satin are the most popular wall finishes, balancing durability and appearance. Semi-gloss and gloss are washable and used for trim, doors, and kitchens/bathrooms. Higher sheen finishes cover slightly less area per gallon because of lower pigment volume.

8. Does primer count as a coat of paint?

Primer is a separate product, not a finish coat. The estimator has a dedicated “Add primer coat” toggle that adds the net wall area once more to the paintable area. Primer is essential when transitioning from dark to light colors, painting over repairs, or covering a glossy existing surface so the new paint adheres properly.

9. How accurate is the paint gallon estimator?

The geometry is exact. The only variability comes from the coverage rate, which depends on paint brand, wall texture, application method, and color. Using the manufacturer’s stated coverage and enabling the waste buffer typically produces estimates within one gallon of actual need for most interior projects.

10. Can I use this calculator for exterior paint?

Not directly. Exterior surfaces like stucco, brick, and siding have very different coverage rates — often 250–350 ft²/gal for rough stucco. You can use the room-by-room approach by treating each exterior wall as a “room” with zero doors/windows where appropriate, but you should set a lower coverage rate to match the exterior product.

11. How do I estimate paint for a room with vaulted or angled ceilings?

Break the room into segments. Measure the shorter wall sections and the taller wall sections separately, then enter them as two “rooms” with the correct heights. Add the ceiling area manually if you are painting it. This segmented approach keeps the geometry accurate for non-rectangular spaces.

12. Should I round up to whole gallons?

Yes. Paint is sold by the gallon, and mixed paint is generally non-returnable. The calculator’s “Round up gallons” toggle enforces whole-gallon purchasing. A result of 2.1 gallons means you must buy 3 gallons — the extra 0.9 gallon is your built-in touch-up supply.

13. How much does a gallon of paint cost?

Interior paint ranges from about $25 per gallon for economy latex to $70+ for premium designer paints, with most quality interior paints landing around $40–$55. Enter your actual per-gallon price in the estimator to get a real material budget. Don’t forget to factor in sales tax using a Sales Tax Calculator for a true total.

14. Can I calculate paint for trim and doors separately?

The estimator focuses on walls and optionally ceilings. For trim, baseboards, and doors, calculate the linear feet of trim multiplied by its width, or count doors and use the 21 ft² figure per door. A separate trim calculation is more accurate than trying to fold it into the wall estimate.

15. Why does textured wall paint cover less area?

Textured surfaces — like knockdown, orange peel, or popcorn — have more physical surface area per square foot of wall because of the peaks and valleys. More surface means more paint absorbed, reducing effective coverage by 10–20%. The estimator’s wall condition dropdown applies this reduction automatically.

16. How do I account for spray application?

Airless sprayers use roughly 25–30% more paint than rollers due to overspray and surface saturation. If you are spraying, reduce the effective coverage rate by about 25% (for example, enter 300 instead of 400) or simply add 25% more gallons by increasing the waste buffer.

17. What happens if I buy too little paint?

You will need to make a second trip to the store, and the new paint may come from a different dye lot, causing a visible color band where the two batches meet. To avoid this, buy all paint at once, enable the waste buffer, and round up to whole gallons. If you must buy more mid-project, request the same batch number.

18. Can I save or print my paint estimate?

Yes. Click the Print Report button to open your browser’s print dialog, where you can save the page as a PDF or send it to a printer. This is useful for taking the estimate to the paint store, attaching it to a client quote, or keeping it with your renovation records.

19. Is one gallon per room a good rule of thumb?

It works only for small to medium bedrooms with standard 8-foot ceilings. It fails for open-concept living areas, great rooms, kitchens, and any room over about 180 ft² of wall area. For multi-room projects, the calculator is far more reliable than any per-room rule of thumb.

20. Does the calculator include labor cost?

No. The cost figure is materials only. Professional labor typically adds 2–3 times the material cost, depending on your region and the complexity of the job. Use the material total as a baseline and get labor quotes separately from local painters.

21. How do I estimate paint for a whole house?

Add every room as a separate entry, set the same coverage rate and finish for consistency, enable the waste buffer, and let the estimator sum the totals. A typical 2,000 ft² home with 8-foot ceilings and two coats usually lands between 12 and 18 gallons for walls only, depending on door and window counts.

22. Can I use quarts instead of gallons for small rooms?

Yes. One gallon equals four quarts. The buying recommendation panel shows an alternative gallons-plus-quarts breakdown for fractional coverage, which is useful for small bathrooms or accent walls where a full gallon is overkill.

23. What coverage rate should I enter for premium paint?

Premium interior paints often state 400–450 ft²/gal. Check the can label and enter that figure in the coverage field. Using a higher coverage rate reduces the gallon estimate, so verify the number matches your specific product to avoid underbuying.

24. Does the calculator work on mobile phones?

Yes. The estimator is fully responsive — the floorplan diagram, bar chart, and breakdown table all adjust to fit smaller screens. You can take measurements on-site with your phone and get an instant estimate without switching devices.

25. How do I account for different paint colors in different rooms?

Calculate each room separately. If rooms use different paint products or finishes, set the coverage rate and finish for each calculation, note the gallons, then switch settings for the next room. The breakdown table helps you keep each room’s quantity distinct for ordering different colors.

Related Calculators

To plan a complete renovation or construction project, these free tools on Calculators4All.com work alongside the Paint Gallon Estimator:

1. Square Footage Calculator — Measure floor and wall area for any room shape.
2. Mulch Calculator — Estimate mulch volume for landscaping around the home.
3. Roofing Calculator — Calculate roof area, shingles, and material costs.
4. Concrete Calculator — Estimate concrete volume and bags for slabs and footings.
5. Board Foot Calculator — Measure lumber for trim, shelving, and framing.
6. Acreage Calculator — Convert area to acres for larger lots.
7. Circle Calculator — Solve area and circumference for circular features.
8. BTU Calculator — Size heating and cooling for the same rooms you are painting.
9. House Affordability Calculator — See what home price fits your budget.
10. Home Equity Loan Calculator — Plan financing for a renovation project.
11. Rental Property Calculator — Model rehab costs against rental income.
12. ROI Calculator — Measure return on a renovation investment.
13. Sales Tax Calculator — Add tax to your paint material budget.
14. Discount Calculator — Calculate savings on bulk paint purchases.
15. Basic Calculator — Quick arithmetic for on-the-fly adjustments.
16. Savings Calculator — Plan savings toward a home improvement fund.

Final Thoughts

Getting the right amount of paint for a multi-room project does not have to be a guessing game. The Paint Gallon Estimator for Multi-Room Floorplans turns room dimensions, openings, coats, and finish choices into a precise, transparent gallon count and material budget — all in one screen, updated live as you type. Whether you are repainting a single bedroom, refreshing a rental unit, or quoting a whole-home repaint, the tool saves money, prevents color-mismatch store runs, and gives you a defensible number to take to the paint counter or attach to a client quote. Add your rooms above, set your finish and coverage, enable the waste buffer, and you will have a trustworthy estimate in minutes — no spreadsheet, no second-guessing, and no leftover gallons gathering dust in the garage.