Paint Calculator
Find out how much paint to buy for a room. Enter the floor size and wall height, take out the doors and windows, pick your number of coats, and see the gallons or litres you need — calculated instantly in your browser, with nothing uploaded.
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Enter the room length, width, and wall height to estimate paint.
How to estimate paint for a room
The calculator works the way a painter would. It finds the total wall area, removes the parts you won't paint, multiplies by how many coats you're applying, and divides by how far one container of paint goes.
Wall area. Add the length and width, double it for the room's perimeter, then multiply by the wall height. A 12 × 10 room with 8-foot walls has 352 square feet of wall.
Doors and windows. Each standard door is roughly 21 square feet and each window about 15 square feet. Enter how many the room has and that area is subtracted, since you don't paint over them.
Coats and coverage. Two coats is the usual choice. One US gallon covers around 350 square feet per coat (about 11 square metres per litre), but textured or unprimed walls drink up more — enter the figure from your paint can for the most accurate result.
Everything runs in your browser — the numbers you type are never uploaded.
Paint calculator questions
How much paint do I need for a room? Multiply the room's perimeter by the wall height for the wall area, subtract doors and windows, multiply by your number of coats, and divide by the paint's coverage. This page does all of that as you type.
How much does a gallon of paint cover? Usually 350–400 square feet per coat on smooth, primed walls. Rough or porous surfaces cover less. The tool defaults to 350 and lets you override it.
How many coats should I use? Two for most repaints and colour changes; one can work when going over a similar colour with quality paint. The default is two coats.
Why subtract doors and windows? Because you don't paint them, so leaving them in overestimates the paint. A standard door is about 21 square feet and a window about 15.
Can I use litres and metres? Yes — switch the units to metric. Dimensions are read in metres and the result is given in litres at about 11 square metres per litre.
This is a planning estimate. Buy a little extra for touch-ups, and round up to whole containers — which the calculator already does.