Enter a room's length, width, and height, plus coats and coverage, to calculate how many gallons of paint you need.

How to Use the Paint Calculator

Enter the room's length, width, and wall height, subtract any doors and windows you don't want painted, and set the number of coats. Coverage per gallon and price per gallon are both editable if your paint's label lists different numbers.

Wall area comes from the room's perimeter times its height — the same geometry used for wallpaper and drywall — paint just adds a coverage rate and a coat count on top.

Wall area = 2 × (Length + Width) × Height
Paintable area = Wall area − Deductions
Total area to paint = Paintable area × Coats
Gallons needed = ⌈Total area to paint ÷ Coverage per gallon⌉

Where 350 Square Feet Per Gallon Comes From

It's a commonly published average across major paint brands for a smooth interior wall, not a guarantee. Textured surfaces, unprimed drywall, and dark or saturated colors all soak up more paint per coat — sometimes closer to 250–300 sq ft per gallon — so check your can's own label and adjust the field if it differs.

Two Coats Is the Default for a Reason

A single coat rarely hides the surface underneath evenly, especially over a different existing color. Going from a dark wall to a light one, or covering a patched section, can call for a third coat — raise the coat count rather than assuming two will always be enough.

Primer and Trim Aren't in This Total

This estimate covers wall paint only. Primer, ceiling paint, and trim paint are typically bought separately and often at a different coverage rate — run them through this same calculator on their own if you need a number for those too.