Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Gallons needed
1.78
Quarts equivalent
7.1
Paintable wall area (sq ft)
333
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter room length (ft).
- 2Enter room width (ft).
- 3Enter ceiling height (ft).
- 4Enter number of doors.
- 5Enter number of windows.
- 6Enter number of coats.
- 7Enter coverage per gallon (sq ft).
- 8Read your gallons needed on the right — it updates as you type.
- 9Hit Share to keep the scenario or send it to someone.
About this calculator
Paint coverage is calculated from wall surface area, minus openings like doors and windows, divided by the coverage rate printed on the can (typically 350-400 sq ft per gallon per coat). This tool computes wall area from room dimensions, subtracts a standard allowance for doors and windows, and multiplies by your number of coats to tell you exactly how many gallons or quarts to buy.
Worked example
Using the values the calculator loads with:
Inputs
- Room length: 12 ft
- Room width: 12 ft
- Ceiling height: 8 ft
- Number of doors: 1
- Number of windows: 2
- Number of coats: 2
- Coverage per gallon: 375 sq ft
Results
- Gallons needed: 1.78
- Quarts equivalent: 7.1
- Paintable wall area (sq ft): 333
What each field means
Inputs
- Room length (ft)
- The room length used in the calculation, measured in ft. Starts at 12 ft so you have a working example on load.
- Room width (ft)
- The room width used in the calculation, measured in ft. Starts at 12 ft so you have a working example on load.
- Ceiling height (ft)
- The ceiling height used in the calculation, measured in ft. Starts at 8 ft so you have a working example on load.
- Number of doors
- The number of doors used in the calculation. Starts at 1 so you have a working example on load.
- Number of windows
- The number of windows used in the calculation. Starts at 2 so you have a working example on load.
- Number of coats
- The number of coats used in the calculation. Starts at 2 so you have a working example on load. Accepted range: 1–4.
- Coverage per gallon (sq ft)
- The coverage per gallon used in the calculation, measured in sq ft. Starts at 375 sq ft so you have a working example on load. Accepted range: 200–500 sq ft.
Results
- Gallons needed
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Quarts equivalent
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Paintable wall area (sq ft)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How much paint do I need for a room?
A 12x12 room with 8-foot ceilings, one door, and two windows has about 320 sq ft of paintable wall area; at two coats and 375 sq ft/gallon coverage, that's roughly 1.7 gallons — round up to two gallons.
Why subtract for doors and windows?
A standard door opening removes about 21 sq ft and a standard window about 15 sq ft of area you don't need to paint, which can be 10-20% of total wall area in a small room.
Do I need two coats?
Two coats is standard for a color change or new drywall. A single coat of the same color as a touch-up may only need one, cutting your gallons roughly in half.
Should I buy extra?
Buy about 10% extra for touch-ups later and to account for textured walls, which soak up more paint than the can's stated coverage rate assumes.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). How Much Paint Do I Need for a Room?. Retrieved from https://www.revenuelab.fyi/toolbox/how-much-paint-do-i-need
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/how-much-paint-do-i-need" target="_blank" rel="noopener">How Much Paint Do I Need for a Room? — RevenueLab</a> (2026).</p>
Source: [How Much Paint Do I Need for a Room? — RevenueLab](https://www.revenuelab.fyi/toolbox/how-much-paint-do-i-need) (2026).