How to use the Paint Calculator
- Enter your room’s length, width and wall height.
- Exclude a door, window or other wall area only if it will remain unpainted; enter its measured size and count.
- See the paintable area and how many gallons or liters to buy.
How much does a gallon of paint cover?
A US gallon of interior paint covers about 350–400 sq ft per coat on smooth, primed walls (about 10–12 m² per liter). Textured, porous or dark surfaces need more. Check the coverage printed on the can and enter it above.
How we calculate
Wall area = perimeter × height. Deduct your measured openings from the walls, add any painted ceiling, then apply the finish and primer coats separately. Each product has its own coverage, reserve and available can sizes. The planner compares least-surplus and lowest-quoted-cost can combinations; missing prices remain unquoted.
Two coats or one?
Use the coat count specified by your chosen product for the surface and colour change. Primer and finish are separate products in this planner, each with its own coverage.
Frequently asked questions
How much paint for a 12×12 room?
With 8 ft walls, one 3×7 ft door, two 3×5 ft windows, two coats and 350 sq ft per US gallon: about 1.90 US gallons before reserve. Adding 10% reserve needs about 2.09 gallons, so the can sizes you choose affect what to buy.
Should I buy extra?
Keep a little for touch-ups — and buy all cans at once so the colour batch matches.