Paint Calculator
Free paint calculator. Estimate gallons and liters of paint for walls and ceilings from room dimensions, coats, and openings. No signup.
A paint calculator estimates how much paint a room needs from its dimensions, coats, and openings, returning gallons and liters so you can buy once instead of making a mid-project trip.
How the coverage is calculated
The calculator builds the paintable area, multiplies by coats, then divides by a coverage rate:
wall area = 2 × (length + width) × height − openingsceiling area = length × width(only if you switch it on)total area = (wall area + ceiling area) × coatsgallons = total area ÷ 350, rounded up, andliters = gallons × 3.785
The 350 ft² per gallon figure is the tool’s assumption for smooth, primed walls. It is fixed, so darker colours, textured surfaces, and bare drywall — all of which absorb more — are not automatically adjusted.
Worked example: a 12 × 10 ft room, two coats
Defaults: length 12 ft, width 10 ft, height 8 ft, 40 ft² of openings, 2 coats, walls only.
| Step | Calculation | Result |
|---|---|---|
| Gross wall area | 2 × (12 + 10) × 8 | 352 ft² |
| Net wall area | 352 − 40 | 312 ft² |
| Area at two coats | 312 × 2 | 624 ft² |
| Gallons | 624 ÷ 350 | 1.78 → 2 gal |
| Liters | 1.78 × 3.785 | 6.7 L |
The exact need is 1.78 gallons, so two one-gallon cans cover it. If you also paint the ceiling, add the 120 ft² floor area to the total before multiplying by coats.
Reference: gallons by room size
Two coats, walls only, with 40 ft² of openings, at 350 ft² per gallon per coat.
| Room (ft) | Net wall area | Area at 2 coats | Gallons (rounded) |
|---|---|---|---|
| 10 × 10 | 280 ft² | 560 ft² | 2 |
| 12 × 10 | 312 ft² | 624 ft² | 2 |
| 12 × 12 | 344 ft² | 688 ft² | 2 |
| 14 × 12 | 376 ft² | 752 ft² | 3 |
| 16 × 14 | 440 ft² | 880 ft² | 3 |
| 20 × 16 | 536 ft² | 1,072 ft² | 4 |
Coverage changes with the surface. Smooth primed drywall is the 350–400 range; bare or unprimed drywall soaks up more, closer to 250–300; heavy texture and masonry can drop below that. When in doubt, round up or plan a separate primer coat.
Primer, sheen, and surface prep
Primer is a separate product with its own coverage, usually lower than topcoat because bare drywall and patched areas absorb it. A dedicated primer is worth the cost when going from dark to light, covering stains or repairs, or painting new board. If you are unsure how much to buy, estimate primer against the same area as one coat of topcoat and check the primer can for its own coverage figure. Sheen matters less for coverage than for durability: flat hides imperfections on ceilings, eggshell and satin handle scrubbing on walls, and semi-gloss suits trim and doors.
Common mistakes
- Forgetting to subtract openings. Doors and windows are real area. The default 40 ft² is roughly a door plus a window.
- Painting one coat over a different colour. One coat rarely covers evenly; the two-coat default exists for a reason.
- Trusting 350 ft² on bare drywall. New board absorbs far more. Prime first and add 10–20%.
- Skipping the ceiling area. It is the same as the floor, and it is easy to forget when only walls are on your mind.
How much paint for a 12 × 10 room?
About 2 gallons for two coats on the walls, assuming roughly 40 ft² of openings. Add the ceiling and you move toward 3 gallons.
How many square feet does a gallon of paint cover?
Roughly 350–400 ft² per coat on smooth, primed walls. This calculator uses 350, which is a safe figure rather than an optimistic one.
Does the calculator include primer?
No. Primer is a separate product with its own coverage, usually lower on bare drywall. Estimate it independently.
How long should I wait between coats?
Water-based wall paint is usually recoatable in two to four hours, though humid conditions slow it down and oil-based products take longer. Follow the can; rushing a recoat is a common cause of an uneven finish.
Paint finishes the surface that drywall sheets create, and if you are considering wallpaper instead, the wallpaper calculator counts rolls from the same measurements.