Paint estimation needs three numbers: total paintable area, number of coats, and the paint's coverage rate (m² per litre). The calculator handles wall area minus doors/windows, optional ceiling, and adds a 5% buffer to the final figure.
What is Paint?
Most interior paints cover 10-14 m² per litre per coat on smooth, primed walls. The number on the can is for ideal conditions — real-world coverage drops on textured walls, dark colours over light, and first coats on raw plaster.
Two coats is the standard for most rooms. Three coats for dark-to-light colour changes or high-traffic walls. Primer counts separately and covers less area (~8 m² per litre).
The calculator deducts standard door (1.6 m²) and window (1.5 m²) sizes from the wall area, optionally includes the ceiling, multiplies by the number of coats, divides by coverage rate, and adds 5% as a buffer for site spillage and brush retention.
Paintable area × coats ÷ coverage
- L, W, H
- Room length × width × height—in metres
- Coverage
- m² per litre—from the paint can label
How to use this calculator
Enter room dimensions and structural openings. Set coats and coverage.
Enter room dimensions
Length, width, and wall height in metres.
Enter doors and windows
Standard sizes assumed (door 0.8×2.0 m, window 1×1.5 m). The calculator deducts these from the wall area.
Decide ceiling
Yes if painting ceiling too. The ceiling area equals the floor area.
Set coats and coverage
Two coats is standard. Coverage 12 m²/L is typical for premium emulsion; 10 for textured; 8 for primer.
Paint scenarios
Single bedroom repaint
10×12 ft × 10 ft height + ceiling. Calculator gives litres for one bucket order.
Whole house repaint
Calculate each room separately, then sum. Order in 20L buckets for cost efficiency.
Exterior walls
Use weather-resistant exterior paint with coverage 8-10 m²/L. Often need 3 coats for full opacity.
Colour change planning
Going dark-to-light or vice versa? Add 1 extra coat — factor that into the calculator.
Glossary
- Coverage
- Square metres painted per litre per coat. Stated on the can; varies by surface.
- Emulsion
- Water-based paint, easier to clean and lower-odour. Standard for interior walls.
- Enamel
- Oil-based paint with a glossy finish. Used on doors, windows, metal.
- Primer
- Base coat that seals raw walls and improves the topcoat's adhesion.