Free paint coverage calculator
Find out exactly how many gallons of paint you need — enter your wall area, number of coats, and surface type and get a whole-gallon count in seconds.
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Estimates only. Actual coverage varies with surface texture, porosity, application method, and paint brand. Always check the manufacturer's label for coverage rates.
Results are estimates. Consult a professional.
How the paint coverage calculator works
Paint is sold by the gallon but used by the square foot, so the calculator bridges those two measures in three steps. First it subtracts the area of any windows and doors from the gross wall area to get the net paintable surface. Then it multiplies that net area by the number of coats you plan to apply. Finally it divides by the paint's coverage rate — how many square feet one gallon covers — and rounds up to the nearest whole gallon, because you can't buy a fraction of a can.
Worked example: two-coat living room repaint
Sofia is repainting her living room. Her walls have a total paintable perimeter of 400 ft². The room has two windows at 15 ft² each (30 ft² total) and one door at 20 ft². She wants two coats on smooth walls at 350 ft²/gal.
Net area = 400 − 30 − 20 = 350 ft². Gallons needed = ⌈ 350 × 2 ÷ 350 ⌉ = ⌈ 700 ÷ 350 ⌉ = ⌈ 2.0 ⌉ = 2 gallons.
Paint gallons needed for common room sizes
The table below shows gallons needed for typical room wall areas at one and two coats, before deducting windows and doors. Subtract roughly 20–40 ft² of openings per room for a closer estimate.
| Wall area (ft²) | Surface | Coverage (ft²/gal) | 1 coat (gal) | 2 coats (gal) |
|---|---|---|---|---|
| 200 | Smooth | 350 | 1 | 2 |
| 200 | Textured | 250 | 1 | 2 |
| 400 | Smooth | 350 | 2 | 3 |
| 400 | Textured | 250 | 2 | 4 |
| 600 | Smooth | 350 | 2 | 4 |
| 600 | Textured | 250 | 3 | 5 |
| 800 | Smooth | 350 | 3 | 5 |
| 800 | Textured | 250 | 4 | 7 |
Gallons rounded up to the nearest whole gallon. Wall area is gross before window and door deductions. Smooth = 350 ft²/gal; textured = 250 ft²/gal.
When to use it and how to measure walls
Getting the gallon count right before you go to the store saves a second trip and avoids leftover paint you can't return. A few measuring habits make the estimate accurate.
- Measure wall height floor-to-ceiling, not floor-to-soffit. Paint goes on the wall face, so use the full wall height — typically 8, 9 or 10 feet for residential rooms.
- Add all four wall perimeters, then multiply by height. For a 12 × 14 ft room with 9 ft ceilings: perimeter = (12 + 14) × 2 = 52 ft; wall area = 52 × 9 = 468 ft². This is your gross area before deductions.
- Deduct each window and door. A standard interior door is roughly 20 ft² (3 ft × 6.7 ft); a double-hung window is typically 12–15 ft². Openings that are less than 10% of the total wall area are often left in the estimate as a buffer.
- Use 350 ft²/gal for smooth walls, 250 ft²/gal for textured. Textured surfaces — popcorn, knockdown, orange peel — absorb more paint. Check your can's label, which always takes precedence over rules of thumb.
- Plan for two coats on color changes. Going from a dark to a light color (or vice versa) almost always needs two coats even with primer. Going from a similar color may need only one.
How accurate is this paint coverage calculator?
The formula math is exact: ceiling division on your measured inputs gives the minimum whole-gallon count that completes the job. There is no approximation in the arithmetic itself — given correct measurements and a known coverage rate, the result is precise.
Real-world accuracy is limited by two factors. First, coverage rates on paint labels range from as low as 200 ft²/gal (high-viscosity primers or very dark saturated colors) to 400 ft²/gal (thin, light-sheen topcoats) — always read your specific product label and use that figure rather than the default. Second, applicator technique matters: a heavily loaded roller or brush soaks more paint into the wall per pass than a lightly loaded one. The calculator uses the label rate as a best-estimate; professional painters often add one extra quart per two gallons as a working buffer. For rooms with intricate trim or moulding, calculate the trim area separately and budget an additional quart per 100 linear feet.
Paint coverage terms defined
About this paint coverage calculator
This calculator runs entirely in your browser — your measurements are never sent to a server, stored, or shared with anyone. It works offline once the page has loaded, so you can use it on-site without a data connection.
Painting a room? Pair this with our square footage calculator to measure wall area, then head to home & garden calculators to browse all tools. Our full library of free calculators covers finance, health, and more.