Paint Calculator
How much paint do you need? Enter your room and watch it come to life — then take the number to the store.
Drag to look around your room
How much paint you need
You'll need about
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How the paint calculator works
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1
Add up the walls
Wall area is the room's perimeter times the wall height. Turn on the ceiling and we add length × width on top.
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2
Take out doors & windows
We subtract a standard 21 ft² per door and 15 ft² per window, so a glassy room doesn't over-buy.
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3
Coats, coverage & a little extra
Multiply by your coats, divide by coverage (≈350 ft²/gal), add 10% for waste, then round up to real tins.
Paint questions, answered
How much paint do I need for a room?
Multiply the room's perimeter by the wall height to get the wall area, subtract about 21 sq ft per door and 15 sq ft per window, multiply by the number of coats, then divide by the paint's coverage (around 350 sq ft per gallon). A typical 12 by 12 ft room with 8 ft walls needs about 2 gallons for two coats. This calculator does all of that instantly as you type.
How much does a gallon of paint cover?
One US gallon of interior wall paint covers roughly 350 to 400 square feet in a single coat on smooth drywall. Primer and rough, porous or textured surfaces are thirstier at about 200 to 300 square feet per gallon. In metric terms a litre covers roughly 10 to 12 square metres. You can adjust the coverage in the advanced options.
Do I need one coat or two?
Plan on two coats for almost any repaint — it gives an even colour and hides the surface underneath. You might get away with one coat when painting a similar colour over a primed or previously painted wall. Big colour changes, or painting over bare or patched surfaces, can need a primer coat plus two finish coats.
Should I subtract doors and windows?
Yes, if you are not painting them. A standard interior door is about 21 sq ft and an average window about 15 sq ft. Subtracting them keeps you from badly over-buying in a room with lots of glass. This calculator subtracts standard sizes automatically based on the counts you enter.
How much extra paint should I buy?
Add about 10% to your estimate for waste, uneven coverage and future touch-ups, then round up to the nearest quart or tin. Keeping a little of the exact colour is far cheaper than trying to match it later. The default already includes a 10% margin, which you can change in the advanced options.
How do I calculate ceiling paint?
Ceiling area is simply the room length times its width. Turn on the ceiling option and this calculator adds it to the total. Ceilings often drink more paint than walls, so if yours is textured, lower the coverage figure a little in the advanced options.