How this paint calculator works
The calculator finds the area of all four walls (the room's perimeter × wall height), subtracts standard openings, adds the ceiling if you choose to, and multiplies by the number of coats. That total is then divided by your paint's coverage rate.
| Imperial | Metric | |
|---|---|---|
| Standard door | 20 ft² | 1.9 m² |
| Standard window | 15 ft² | 1.4 m² |
| Typical coverage | 350–400 ft² per gallon | 9–11 m² per liter |
How many coats of paint do I need?
Two coats is the standard for most rooms – it gives even color and better durability. One coat can be enough when repainting the same color over a clean wall. Plan on three coats (or a primer plus two coats) when covering a dark color with a light one or painting fresh drywall.
How much does a gallon of paint cover?
Most interior wall paints cover about 350–400 square feet per gallon in one coat. Check the label on the can: the manufacturer's figure is the most accurate number to put in the coverage field.
Should I buy extra paint?
Yes – keep a little left over for touch-ups. Paint mixed in different batches can vary slightly, so buying everything at once avoids visible color differences.
How much paint for a 12×12 room?
A 12×12 ft room with 8 ft walls, one door and two windows has about 334 ft² of wall. With two coats that's roughly 1.9 gallons, so two gallons will do the walls.