Calculators/ Interior/Paint Calculator
Paint Calculator
Gallons of paint and primer for a room.
Paint Calculator
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A gallon covers about 350 square feet on smooth drywall, but far less on texture, bare drywall or anything porous. Two coats is the realistic default: one coat only works when repainting a similar colour.
How this is calculated
- Paintable area = perimeter × height, minus doors and windows. Add the ceiling if you are painting it.
- Multiply by the number of coats, then divide by the coverage rate.
- Drop the coverage rate for texture or porous surfaces. New, unprimed drywall soaks up roughly twice as much on the first coat, which is why priming is cheaper than painting three times.
Frequently asked questions
How much does a gallon of paint cover?
About 350 square feet on smooth, previously painted drywall. Expect 250 to 300 on texture, and considerably less on bare drywall or masonry.
Do I need primer?
Yes on new drywall, over bare wood or patches, and when making a drastic colour change. Primer is cheaper than paint and stops the finish coat soaking in unevenly.
Should I deduct doors and windows?
Deduct anything over about 15 square feet. Smaller openings roughly cancel out against the extra paint used cutting in around them.