Calculators
Paint calculator
Runs in your browser · does not check building standards
How much paint you need for a room, in gallons and quarts, from the room size, coats and the coverage on the can.
Result
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How it was calculated
How to use
- Measure the room: Length, width and ceiling height in feet.
- Count openings: Doors and windows are deducted with typical sizes.
- Read the can: Enter the coverage per gallon from the label and the number of coats.
- Buy: Use the suggested gallons and quarts, all from the same batch.
How it is calculated
- Wall area = 2 × (length + width) × ceiling height
- Area to paint = wall area − doors (20 sq ft each) − windows (15 sq ft each) + ceiling if included
- Gallons = area × coats ÷ coverage per gallon × surface factor
- Buy = gallons + 5%, packed into 5-gallon pails, gallons and quarts
Examples
12 × 10 ft bedroom, two coats
Walls 352 sq ft minus one door and two windows = 302 sq ft. Two coats at 350 sq ft per gallon = 1.73 gallons, so buy 2 gallons.
Same room with the ceiling
302 sq ft of wall plus 120 sq ft of ceiling = 422 sq ft. Two coats = 2.41 gallons; with 5% for touch-ups that is 2.53, so buy 3 gallons (three quarts would cost more than a third gallon).
Frequently asked questions
How many square feet does a gallon of paint cover?
Interior paint cans typically state roughly 250 to 400 sq ft per gallon per coat; 350 is a common middle value. Rough, porous or unprimed surfaces get less, so use the lower figure for them.
How much paint do I need for a 12 × 12 room?
With an 8 ft ceiling the walls are 384 sq ft; minus a door and a window that is about 349 sq ft. Two coats at 350 sq ft per gallon need about 2 gallons; with a small reserve, buy 2 gallons and 1 quart.
Do I need two coats?
Usually yes for an even finish, especially when changing color. One coat can be enough when repainting the same color over a sound surface.
Should I buy a 5-gallon pail?
Once you need more than about four gallons, a 5-gallon pail is usually the better buy and keeps the color consistent. The calculator switches to a pail at that point.
Keep planning with your measurements
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