Paint Calculator
Calculate how much paint a room needs. Enter the room size, the number of doors and windows, and how many coats you plan to apply.
Short answer: One gallon of paint covers about 350 sq ft per coat. A typical 10 ft × 12 ft bedroom with an 8 ft ceiling needs about 2 gallons for two coats.
Fill in the fields above to see your result.
Two coats is standard, and is required when changing colour significantly. Check your paint label — some products cover 400 sq ft per gallon.
How this paint calculator works
Every material here comes down to a volume. The area is measured in square feet, the depth is converted from inches to feet, and the result is converted from cubic feet into the unit you actually buy in — cubic yards, tons, or bags.
length (ft) × width (ft) = sq ftsq ft × depth (in) ÷ 12 = cubic feetcubic feet ÷ 27 = cubic yardsBag counts on this page are rounded up to whole bags, because you cannot buy part of a bag. Rounding up also gives you a little spare material, which is what you want on a real job.
Paint for common rooms (2 coats, 8 ft ceiling, 1 door, 2 windows)
| Room | Net wall area | Paint needed | Buy |
|---|---|---|---|
| 10 ft × 10 ft | 269 sq ft | 1.54 gal | 2 gallons |
| 10 ft × 12 ft | 301 sq ft | 1.72 gal | 2 gallons |
| 12 ft × 14 ft | 365 sq ft | 2.09 gal | 3 gallons |
| 16 ft × 20 ft | 525 sq ft | 3.00 gal | 3 gallons |
Wall area deducts one standard door (21 sq ft) and two standard windows (15 sq ft each). Ceiling paint is calculated separately.
Frequently asked questions
How much square footage does a gallon of paint cover?
Most interior paints cover 350 to 400 sq ft per gallon per coat. This calculator uses 350 sq ft, which is the conservative figure and the one most paint labels quote for a smooth surface.
Do I need one coat or two?
Two coats for a colour change, for a fresh or patched wall, or for any deep or saturated colour. One coat is sometimes enough when you are repainting the same colour over a clean, sound surface.
How much paint for a 12x12 room?
A 12 ft by 12 ft room with an 8 ft ceiling has roughly 333 sq ft of wall area once one door and two windows are deducted. Two coats needs about 1.9 gallons, so buy 2 gallons.
Do I need to subtract windows and doors?
Yes. Deduct about 21 sq ft for a standard door and about 15 sq ft for a standard window, then deduct more for large openings. This calculator does that for you.
How much paint for a ceiling?
Multiply the room length by the width. A 12 ft × 12 ft ceiling is 144 sq ft, which is well under one gallon per coat. This calculator covers walls only.
Other calculators
These figures are estimates for planning only. Bag sizes, stone densities and paint coverage vary by product and supplier, so check the label or ask your yard before you order. Last updated 2026-09-30.