Square Footage Calculator
Calculate how many gallons of paint you need based on room size.
Calculate how many gallons of paint you need based on room size.
The one number nearly every project starts with. Work out the square footage of a room and turn it straight into gallons of paint, boxes of tile, or boxes of flooring.
For paint, the wall area is the perimeter times the height — 2 × (length + width) × height — with roughly 20 square feet subtracted per door and 15 per window. That paintable area, multiplied by the number of coats and divided by the coverage on the can (typically 350 square feet per gallon), gives the gallons. For floors, the area is simply length × width, plus a waste allowance because tile and plank both generate offcuts.
Example
A 12 × 14 foot room with 8-foot ceilings has 416 square feet of wall. Take out one door and two windows and you are painting about 366 square feet — two coats is 732 square feet, or three gallons at 350 square feet per gallon.
About three gallons for two coats on the walls, assuming 8-foot ceilings and standard coverage of 350 square feet per gallon. Add roughly a gallon and a half if you are also painting the ceiling.
Ten percent for a straight layout, and 15 to 20 percent for a diagonal or herringbone pattern, which produces far more offcuts. Order it all in one go so the batch matches.
On a smooth, sealed, similar-colored wall, roughly. On new drywall, over a dark color, or on texture, expect meaningfully less — plan closer to 250 to 300 square feet per gallon.