Estimate how many gallons of paint you need for room walls.
Rooms are painted over their wall perimeter times the wall height, with door and window openings subtracted. Multiplied by the number of coats and divided by the coverage of one gallon, this gives the gallons to buy. Painting uses roughly one coat to an even primer before asking your color of coverage, and buying the right amount avoids both waste and a second trip to the store.
Paint Needed
Gallons = (perimeter x wall height - openings) x coats / coverage
Gallons = (perimeter x wall height - openings) x coats / coverage Rooms are painted over their wall perimeter times the wall height, with door and window openings subtracted. Multiplied by the number of coats and divided by the coverage of one gallon, this gives the gallons to buy.
Painting uses roughly one coat to an even primer before asking your color of coverage, and buying the right amount avoids both waste and a second trip to the store.
This calculator takes 7 inputs: Room width, Room length, Wall height, Door openings, Window openings, Coats, Coverage. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.