Paint Calculator – Gallons Needed for Walls
Free paint calculator: enter wall dimensions, number of walls, coats and coverage to estimate gallons of paint needed. No sign-up, runs in your browser.
Paint Calculator
Estimate paint needed for walls. Enter dimensions in feet. Coverage is typically 350–400 sq ft per gallon.
How the paint calculator works
gallons = (wall_length × wall_height × num_walls × coats) ÷ coverage_per_gallon
Coverage is usually 350–400 sq ft per gallon per coat. Result is rounded up to the nearest tenth of a gallon.
Estimating paint for interior and exterior walls
Buying the right amount of paint avoids extra trips to the store and leftover cans that go to waste. A paint calculator takes your wall dimensions, multiplies by the number of walls and coats, and divides by the coverage rate to give you gallons needed. Coverage varies by product: premium paints often cover more per gallon, while budget options may need more. Check the label on your chosen paint.
For a rectangular room, measure one wall’s length and height. If walls differ, either average them or calculate each wall separately and add. Doors and windows reduce the area; for a quick estimate you can ignore them, but for accuracy subtract their area. Two coats are standard for good coverage and durability. Dark colors or dramatic changes may need a third coat or a tinted primer.
Exterior paint often has different coverage and may need more for rough surfaces. Always buy a little extra for touch-ups; paint stores can match a batch if you keep the code. Use our area calculator to find wall area if you have complex shapes, and the tile or brick calculators for other finishing projects.