The basic math
A gallon covers roughly 350–400 square feet on smooth, previously painted drywall. Textured stucco, knockdown, and rough wood can drop that to 200–250. Deep colors over light walls usually need two coats regardless.
Measure the perimeter of the room, multiply by ceiling height, then subtract about 20 square feet per door and 15 per window.
Use the calculator
Our coverage calculator handles the arithmetic, the second coat, and the surface allowance, and tells you which can sizes to buy.
Buy the tint in one batch
Custom-tinted colors can vary slightly batch to batch. Buy everything for a job at once, or box multiple gallons together before you start.