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Construction — Interiors
Paint Calculator
Enter your room size, number of coats, and doors and windows to get how many gallons of paint you need.
Paint needed
—
One gallon covers about 350 sq ft.
| Paintable wall area | — |
|---|---|
| Gallons (exact) | — |
| Quarts if buying small | — |
Show our math
Enter your figures above to see the step-by-step working.
An estimate — rough or new drywall needs more; walls onlyEverything computed client-side — nothing leaves this page
How the Paint Calculator Works
The calculator finds the total wall area — twice the room’s length plus width, times the wall height — then subtracts a standard allowance for each door (about 21 sq ft) and window (about 15 sq ft). Multiply by the number of coats, divide by the paint’s coverage, and round up to whole gallons.
Most interior paints cover roughly 350 square feet per gallon on a smooth, previously painted wall. Rough, porous or brand-new drywall drinks more, and dark-to-light colour changes may need an extra coat.
gallons = wall area × coats ÷ coverage per gallon
Frequently Asked Questions
How much paint do I need for a room?
Find the wall area (twice the length plus width, times the height), subtract for doors and windows, multiply by the number of coats and divide by about 350 square feet per gallon. A 12 by 10 room with 9-foot walls needs roughly 2 gallons for two coats.
Does the calculator include the ceiling?
No, it estimates the walls only. To paint the ceiling too, add its area (length times width) to your total and buy paint for it separately, as ceiling paint often differs.
Why round up to whole gallons?
Paint is sold in gallons and quarts, and it is better to have a little left for touch-ups than to run out mid-wall and risk a colour-batch mismatch. The calculator shows the exact figure and the rounded-up amount.
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