Paint Calculator
Free paint calculator that turns wall area, number of coats, and coverage into the gallons of paint you need. Use it as a paint coverage calculator for interior or exterior projects and round up to whole cans.
Calculate paint gallons
How the paint calculator works
This paint calculator is built on a simple area equation: wall area × coats ÷ coverage. Say you have 200 sq ft of wall and want one coat at 350 sq ft per gallon — that is 200 × 1 ÷ 350 = 0.57 gallons, so you would buy one gallon. As a paint coverage calculator it lets you match the exact coverage rate printed on your product, which varies between brands and finishes.
Use it as an interior paint calculator for bedrooms and living spaces, or as an exterior paint calculator for siding and trim — the math is the same, you just enter the relevant area and a coverage rate suited to the surface. Working in square feet? It is also a paint calculator square feet tool: every input is in square feet so there is no unit conversion.
Coats, coverage and texture
Two factors change your gallons the most: coats and surface. New drywall or a dark-to-light color change usually needs two coats. Smooth walls take paint efficiently at about 350 sq ft per gallon, while textured or porous surfaces drop to 250–300, so an honest paint coverage calculator uses the real rate rather than a best case. Always round up to whole cans, and keep a little extra for touch-ups.
How to use this calculator
- Measure the wall area. Add up the area of every wall you plan to paint, in square feet. This paint calculator lets you subtract big openings — about 21 sq ft per door and 15 sq ft per window — for a tighter estimate.
- Choose coats and coverage. Pick one coat for a refresh or two for a color change. Enter the coverage rate from the can; this paint coverage calculator defaults to 350 sq ft per gallon for smooth walls and less for texture.
- Calculate gallons. The tool multiplies area by coats and divides by coverage. As an interior paint calculator it reports the exact gallons and rounds up to whole cans so you do not run short mid-wall.
- Estimate paint cost. Enter a price per gallon and the paint cost calculator multiplies it by the whole cans you need, giving a quick budget for the project.
Frequently asked questions
How does the paint coverage calculator handle two coats?
It multiplies the wall area by the number of coats first, then divides by the coverage rate. Two coats simply doubles the area you are painting.
What coverage should I use as an interior paint calculator?
About 350 sq ft per gallon for smooth interior walls. Drop to 250–300 sq ft per gallon for textured or porous surfaces.
Can I use this as an exterior paint calculator?
Yes. Enter your siding area and a coverage rate suited to the surface; rough exterior textures use more paint than smooth interior drywall.
Why does the result round up?
Stores sell paint by the can, so the paint cost calculator rounds up to whole gallons and leaves a little extra for touch-ups.
Does it work in square feet only?
Yes — it is a paint calculator square feet tool. Every field is in square feet, so there is nothing to convert.
Gallons by area and coats
| Wall area | Coats | Gallons (350 sq ft/gal) |
|---|---|---|
| 200 sq ft | 1 | 0.57 → 1 gallon |
| 400 sq ft | 2 | 2.29 → 3 gallons |
| 1,000 sq ft | 2 | 5.71 → 6 gallons |
One gallon is the practical minimum for any real wall, even when the math says less.