Paint calculator
Paint = area × coats ÷ spread rate. A 12 × 12 ft room with 8 ft walls has 384 ft² of walls: two coats take about 1.9 to 2.2 gallons.
- Checked on thousands of cases
- Sources: Sherwin-Williams
- Updated November 5, 2026
Doors and windows, total area
Optional, printed on the can
Paint needed
Area to paint: 384 ft²
Range based on a published spread rate of 350–400 ft²/gal (Sherwin-Williams SuperPaint Interior Latex Flat). Enter your paint's rate for a single figure.
= 1 gal
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How it works
Formula: Paint = area × coats ÷ spread rate
The calculator adds up the four walls (2 × (length + width) × height), adds the ceiling if you tick it, and subtracts the doors and windows you enter. It multiplies by the number of coats and divides by the spread rate of the paint. By default it uses the rate published by Sherwin-Williams for its SuperPaint Interior Latex Flat: 350 to 400 ft² per gallon, which is why the result is a range. Spread rates vary between products and with porous or textured surfaces: enter the one printed on your can for a precise result.
Paint for the walls of a room, two coats
| Room | Wall area | Paint |
|---|---|---|
| 10 × 10 ft | 320 ft² | 1.6–1.8 gal |
| 12 × 12 ft | 384 ft² | 1.9–2.2 gal |
| 14 × 12 ft | 416 ft² | 2.1–2.4 gal |
| 16 × 14 ft | 480 ft² | 2.4–2.7 gal |
Frequently asked questions
How much paint do I need for a room?
Measure the walls: 2 × (length + width) × height. For a 12 × 12 ft room with 8 ft walls, that is 384 ft². With two coats and 350 to 400 ft² per gallon, plan 1.9 to 2.2 gallons.
How many coats of paint?
The Sherwin-Williams data sheet for SuperPaint lists two coats on drywall, wood and plaster. A strong color change can need a primer first.
Should I subtract doors and windows?
Yes, for large openings: enter their total area in the 'Openings' field. Small ones can be ignored; they make a small margin.