Paint Calculator
Calculate liters of paint needed for walls, accounting for doors and windows.
Construction
Paint Calculator
Generated on April 24, 2026
Room (meters)
Paint Required
NaN liters
Step-by-step calculation
Formula
Wall area = 2·(W + L)·H. Paint liters = paintable × coats ÷ coverage.
- 1Perimeter = 2 × (NaN + NaN) = NaN m
- 2Wall area = NaN × NaN = NaN m²
- 3Openings = 1 × 1.85 (doors) + 2 × 1.5 (windows) = 4.85 m²
- 4Paintable area = NaN − 4.85 = NaN m²
- 5Paint = NaN × 2 coats ÷ 10 m²/L = NaN L
?What is the Paint Calculator?
A paint calculator estimates how much paint you need to cover the walls of a room, taking into account the room's dimensions, the number of doors and windows to subtract, the number of coats required, and the paint's advertised coverage rate (typically 10 m² per liter for smooth walls). This is essential for homeowners, painters, and renovation planners who want to buy enough paint to finish the job in one trip without significant leftovers — or the far worse alternative of running out mid-project when the paint store is closed.
The Formula
The total wall area equals the room's perimeter multiplied by its ceiling height. Subtract the area of each door (typically 1.85 m² for a standard interior door) and each window (approximately 1.5 m² for a mid-sized window). Multiply by the number of coats you plan to apply — usually two for a new paint color and one for a touch-up — then divide by the paint's advertised coverage rate. Textured or porous walls reduce effective coverage by 20–30%, so adjust the coverage figure downward for those surfaces.
Practical Examples
A 4 × 5 m room with 3 m ceilings has 54 m² of wall area; at 2 coats and 10 m²/L coverage, you need 10.8 L of paint — roughly three 4-L cans.
Standard interior door openings (1.85 m²) and standard windows (1.5 m²) reduce the paintable area — a typical bedroom loses 3–5 m² to these.
Primer counts as one coat and usually adds 5–8 m²/L coverage depending on the surface, so new drywall often needs primer plus 2 top coats.
Textured walls (popcorn ceilings, stucco, rough plaster) absorb 20–30% more paint than smooth drywall — budget accordingly.
Dark paint over light (or vice versa) often needs 3 coats for complete opacity — calculate assuming 3 coats for strong color changes.
Exterior paint usually has lower coverage (5–7 m²/L) than interior due to weather-protective thickness — use the exterior number from the can.