One gallon covers about 350 ft² per coat, so most rooms take one to two gallons for two coats after subtracting doors and windows.
MEASURE. ESTIMATE. BUILD.
Paint Calculator
Enter your wall area to find how many gallons of paint you need.
01 / PROJECT DIMENSIONS↙
Total wall length
Wall height
Waste %%
Change any measurement to update your estimate.
02 / YOUR MATERIAL ESTIMATE
You need approximately
1 gallon
covers 336 ft² (incl. waste)
- Area to cover
- 336 ft²
- Exact amount
- 0.96 gallons
Field notes
Always calculate for the coats you'll actually apply — nearly every color change needs two, and primer is a separate gallon on bare drywall or a big color jump. The 350 ft²/gallon spread rate assumes primed, smooth walls; textured or porous surfaces drink more, so round up. Box your paint (combine cans into one bucket) so the color stays consistent wall to wall.
How the paint calculator works
The math behind the tool:
gallons = wall area ÷ 350 × coats × (1 + waste%)Sources: U.S. EPA — Indoor Air Quality (low-VOC interior paint and indoor air quality).
Frequently asked questions
How much paint do I need for a room?
Multiply the room perimeter by the wall height for total area, subtract doors and windows, then divide by 350 ft² per gallon and multiply by the number of coats. A 12×12 room usually needs about 2 gallons for two coats.
How many square feet does a gallon of paint cover?
One gallon of interior paint covers about 350–400 ft² in a single coat on primed, smooth walls; textured or porous surfaces cover less.
How do you calculate how much paint to buy?
Add up the wall length, multiply by the ceiling height for total wall area, then divide by 350 — the square feet one gallon covers in a single coat. Multiply by the number of coats. Do not subtract small windows and doors; the offcuts and touch-ups absorb the difference.
How do you calculate square footage for painting?
Measure the perimeter of the room and multiply by the wall height. A 12 by 14 room has a 52-foot perimeter, so at 8 feet that is 416 square feet of wall. Add the ceiling separately — length × width — if you are painting it too.
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