Paint Calculator
Gallons of paint = paintable area × number of coats ÷ the spread rate on the can — 350 ft² per gallon by default for smooth, primed drywall. Two coats on 220 ft² of wall is 440 ft², or 1.26 gallons: buy a gallon and a quart. To deduct doors and windows for you, use the Wall Paint Calculator.
How it's calculated: Gallons = (paintable area × coats) ÷ spread rate (default 350 ft² per gallon per coat).
Result appears here
Fill in the fields and press Calculate.
Formula, calculation, assumptions and sources
Gallons = (Paintable area × coats) ÷ spread rate
Spread rate ≈ 350 ft² per gallon per coat
Run the calculation to see each step with your own numbers.
220 ft² of wall, 2 coats, 350 ft²/gal.
Coverage = 220 × 2 = 440 ft²
Gallons = 440 ÷ 350 = 1.26 → buy 1 gal + 1 qt (or round to 2 gal)
- Spread rate is the manufacturer's figure for your paint and surface — the default 350 ft²/gal suits smooth, primed drywall.
- Bare drywall, masonry or a big colour change needs a primer coat, which is extra.
- Trim, doors and ceilings are separate — this is the wall field.
- No 'recommended' allowance is added: rounding up to whole cans plus a little left for touch-ups covers it.
- Why does the calculator say 1.26 gallons — do I buy 2?
- Buy a gallon plus a quart (a quart covers ~90 ft²). Many stores sell quarts; it's cheaper than a second gallon and you'll still have touch-up paint.
- Do I need a separate primer coat?
- Yes, over bare drywall or masonry, or for a big colour change or a stain. Primer is a full coat of its own — add one to the coat count, or run the calculator again for the primer at its own spread rate.
- How much paint do I need for a room?
- Multiply the wall area (doors and windows deducted) by the number of coats and divide by the spread rate on the can — about 350 ft² per gallon on smooth, primed walls. 220 ft² of wall at two coats needs 1.26 gallons.
- How many square feet does a gallon of paint cover?
- Around 350–400 ft² per coat on a smooth, primed surface, per manufacturer data sheets, and 250–300 ft² on textured, masonry or bare drywall. The Paint Coverage Calculator works the other way — the area a given amount of paint covers.
Spread rate
≈ 350 ft² per US gallon per coat for interior latex on a primed, smooth surface. Paint-manufacturer data sheets (Sherwin-Williams, Benjamin Moore) quote 350–400. Rougher/porous surfaces are lower. Editable.
About the Paint Calculator
The Paint Calculator turns a paintable wall area and a number of coats into gallons of paint, using a spread rate you set — the default 350 ft² per gallon suits smooth, primed drywall, but a textured or bare surface is lower. It adds no waste allowance because rounding up to whole cans covers touch-ups. Trim, doors and ceilings are separate; for walls with the openings deducted for you, use the Wall Paint Calculator.
What you enter
- Wall area to paint — Total wall area with doors and windows already deducted — use the Wall Square Footage Calculator.
- Coats
- Coverage (ft² per gallon per coat) — Manufacturer's spread rate. 350–400 for smooth walls; 250–300 for textured, masonry or bare drywall.
- Deduct for openings — If you entered the gross wall area, deduct a percentage for doors/windows here (a typical room is 10–15%).
What you get back
- Paintable area — the exact result of the calculation.
- Paint needed — Round up to whole cans — a gallon and a quart is often cheaper than two gallons.
The formula, a worked example, the assumptions behind it and the sources are shown in full below the calculator.
Related calculators
- Wall Paint Calculator — Paint for walls only, with doors and windows deducted.
- Ceiling Paint Calculator — Paint for a ceiling of a given area and number of coats.
- Paint Coverage Calculator — Area a given amount of paint will cover, or paint needed for an area.
- Wall Square Footage Calculator — Wall area for one or more walls, with openings deducted.
Related articles
- How Much Paint Coverage Should You Expect? — Paint coverage is usually stated per gallon on the can, but surface texture, porosity and application method can all shift real-world coverage.
Part of the Painting calculators.