Paint Calculator
Enter your room size to get the paint you need in gallons and litres, plus an estimated cost.
Paint needed
Estimated cost
How to calculate paint for a room
Paint is sold by volume, so first find the wall area. For a rectangular room, add length and width, double it, and multiply by wall height. Multiply by the number of coats, then divide by the coverage per gallon.
Formula: gallons = 2 × (length + width) × height × coats ÷ coverage per gallon, rounded up
Worked example: 12 ft × 10 ft room, 8 ft walls, 2 coats
Wall area = 2 × (12 + 10) × 8 = 352 sq ft. With 2 coats: 704 sq ft. At 350 sq ft per gallon: 704 ÷ 350 = 2.01, rounded up to 3 gallons.
Doors and windows
This calculator counts full walls, so you get a little extra paint for touch-ups. If you want an exact figure, subtract about 20 sq ft per door and 15 sq ft per window from the wall area.
How many coats?
Two coats is the standard for even colour and durability. One coat can work for a refresh over the same colour. New drywall and big colour changes need a primer coat first.
Common room sizes
Cost tips
Prices on this page are editable estimates, not quotes. Get 2 to 3 local quotes before you buy, and ask if delivery is included. Delivery, tax and waste can change the total a lot. Order a little extra for cuts and breakage, and confirm final quantities with your supplier or a qualified professional.
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Frequently asked questions
How much paint do I need for a 12x12 room?
A 12 ft by 12 ft room with 8 ft walls needs about 3 gallons for 2 coats, at 350 sq ft per gallon.
How many coats of paint do I need?
2 coats for most walls. Use 1 coat only for a refresh over the same colour, and a primer coat for new drywall or big colour changes.
How much area does a gallon of paint cover?
About 350 sq ft per coat on smooth walls. Rough or porous walls use more.
Are doors and windows subtracted?
No, this calculator counts full walls. That leaves a little extra paint, which is useful for touch-ups. A door is about 20 sq ft and a window about 15 sq ft.
Do I need primer?
Yes on new drywall, patched walls, and dark-to-light colour changes. On already painted walls in good shape, you can often skip it.
Are the prices accurate?
Prices are editable estimates. The defaults are typical US figures, and your local price can be higher or lower.