Paint Calculator
Room length, width, and wall height in; doors and windows deducted; coats and coverage applied — out comes the wall area and the gallons, rounded up, because being a quart short means a second trip to the store.
Planning tool — results are estimates for quoting and ordering, not engineering or building-code advice.
Common questions
How much does a gallon cover?
Most interior paints cover 300–400 sq ft per gallon per coat on smooth, primed walls — the default here is 350. Drop it for rough or porous surfaces and first coats on new drywall.
How are doors and windows handled?
Standard deductions: about 21 sq ft per door and 15 sq ft per window, subtracted from the wall area before coats are applied.
Why does it round gallons up?
Paint is bought in whole cans. The calculator rounds up so the number you see is the number you buy.
Related: Stairkey for painting businesses · Free painting estimate template
More free calculators
All 14 are free, feet-and-inches in, no sign-up. Pick the next one for the job.
Concrete & site work
Finishes & materials
This solves one measurement. The Takeoff Builder prices the whole job.
Walk the rooms, enter dimensions, and formula-driven scope turns measurements into quantities, prices, and the estimate itself — from $20/mo, capped, no surprise bills.