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
Paint needed (gallons)
2.0
Gallon cans to buy
2
Estimated paint cost
$96
Paintable wall area (sq ft)
345
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter room perimeter (ft).
- 2Enter ceiling height (ft).
- 3Enter doors.
- 4Enter windows.
- 5Enter coats.
- 6Enter coverage per gallon (sq ft).
- 7Enter price per gallon ($).
- 8Read your paint needed (gallons) on the right — it updates as you type.
- 9Hit Share to keep the scenario or send it to someone.
About this calculator
A gallon covers roughly 350 square feet per coat on primed drywall. Dark colours over light walls almost always need two coats, and fresh drywall needs primer on top of that.
Worked example
Using the values the calculator loads with:
Inputs
- Room perimeter: 48 ft
- Ceiling height: 9 ft
- Doors: 2
- Windows: 3
- Coats: 2
- Coverage per gallon: 350 sq ft
- Price per gallon: 48 $
Results
- Paint needed (gallons): 2
- Gallon cans to buy: 2
- Estimated paint cost: $96.00
- Paintable wall area (sq ft): 345
What each field means
Inputs
- Room perimeter (ft)
- The room perimeter used in the calculation, measured in ft. Starts at 48 ft so you have a working example on load.
- Ceiling height (ft)
- The ceiling height used in the calculation, measured in ft. Starts at 9 ft so you have a working example on load.
- Doors
- The doors used in the calculation. Starts at 2 so you have a working example on load.
- Windows
- The windows used in the calculation. Starts at 3 so you have a working example on load.
- Coats
- The coats used in the calculation. Starts at 2 so you have a working example on load. Accepted range: 1–4.
- Coverage per gallon (sq ft)
- The coverage per gallon used in the calculation, measured in sq ft. Starts at 350 sq ft so you have a working example on load.
- Price per gallon ($)
- The price per gallon used in the calculation, measured in $. Starts at 48 $ so you have a working example on load.
Results
- Paint needed (gallons)
- 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.
- Gallon cans to buy
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Estimated paint cost
- Returned as a money amount in US dollars. 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 does the paint calculator work?
A gallon covers roughly 350 square feet per coat on primed drywall. Dark colours over light walls almost always need two coats, and fresh drywall needs primer on top of that. The underlying maths is: Gallons = (Wall area − openings) × Coats ÷ Coverage per gallon.
What do I need to enter?
7 values: room perimeter, ceiling height, doors, windows, coats, coverage per gallon, and price per gallon. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the paint needed (gallons) result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Estimates assume standard, average conditions — local rules, pricing, and materials vary.
Who is this tool for?
It's built for anyone doing everyday planning maths — a quick estimate that would otherwise need four browser tabs and a calculator app.
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). Paint Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/paint
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/paint" target="_blank" rel="noopener">Paint Calculator — RevenueLab</a> (2026).</p>
Source: [Paint Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/paint) (2026).