MaterialScopeHow much paint for a 12 × 12 room?
Wall height, openings, coats and coverage matter just as much as the floor size.
Measure the walls
The perimeter is 2 × (12 + 12) = 48 feet. Multiply by 8-foot height to get 384 square feet of walls. Subtract the assumed 42 square feet of doors and windows to get 342 square feet of paintable wall.
Apply coats and coverage
342 × 2 ÷ 350 × 1.10 = 2.1497 gallons. The can count rounds up after the allowance. Change coverage to match your paint and surface. Paint sold in quarts or larger containers may offer another purchasing combination.
Decide whether to include the ceiling
The ceiling adds 144 square feet. If painted with the same product and two coats, the same assumptions produce 3.0549 gallons, rounded to four. If using a different ceiling paint, calculate and purchase it separately.
Keep trim and primer on their own list
This wall estimate does not include doors, baseboards, cabinets or primer. Color changes and substrate condition can alter the required product and coats. Follow the selected paint’s preparation and application instructions.
Taller walls change the answer
A 12 × 12 floor plan says nothing about wall height. The table keeps the same openings, two coats, 350 ft²/gal coverage and 10% allowance while changing only the height.
| Wall height | Paintable walls | Walls only | Walls + ceiling |
|---|---|---|---|
| 8 ft | 342 ft² | 2.15 gal → 3 cans | 3.05 gal → 4 cans |
| 9 ft | 390 ft² | 2.45 gal → 3 cans | 3.36 gal → 4 cans |
| 10 ft | 438 ft² | 2.75 gal → 3 cans | 3.66 gal → 4 cans |
One coat instead of two
A single coat over the same 342 ft² of walls calculates to 1.07 gallons with 10% extra, which rounds up to 2 one-gallon cans. The extra fraction is small, so compare a gallon plus a quart if your store sells both. Whether one coat is enough depends on the product, the color change and the surface.
Product reference: Sherwin-Williams paint calculator guidance. Confirm the current label for your chosen product.
Change the measurements and allowance to match your plan.
Open Room Paint CalculatorMaterialScope editorial · Updated September 29, 2026 · Calculation methodology