Find out how many gallons of paint you need based on wall dimensions, doors, windows, and the number of coats.
Enter the width and height of the wall (or add up the total width of all walls in a room), the number of standard doors and windows to subtract, how many coats you plan to apply, and the coverage rate listed on your paint can. Click "Calculate Paint Needed" for your estimate.
Paintable area = (width × height) - (doors × 21 sq ft) - (windows × 15 sq ft), using standard average sizes for doors and windows. Total area to cover = paintable area × number of coats. Gallons needed = total area ÷ coverage per gallon.
A 15 ft by 9 ft wall (135 sq ft) with one door and one window has a paintable area of about 99 sq ft. Applying 2 coats requires covering 198 sq ft, which needs a little under 1 gallon at a coverage rate of 350 sq ft per gallon.
Should I round up when buying paint? Yes, always round up to the next full can or gallon, and consider buying slightly extra for touch-ups and future repairs since color batches can vary.
Does texture or wall color change the coverage? Yes, textured surfaces and drastic color changes (like painting over a dark wall with a light color) can reduce actual coverage, so check your specific paint can's guidance.
Total wall area divided by the paint's coverage rate (commonly 350-400 sq ft/gallon).
Most surfaces need two coats for even coverage, roughly doubling paint needed.
Yes — textured or porous surfaces absorb more paint and cover less area per gallon.