How much paint do I need? The answer depends on wall area, coverage rate, and coats.
The Formula
Paint (L) = Paintable area (m²) × Coats ÷ Coverage (m²/L)
Step 1: Measure Walls
Wall area = Perimeter × Height = 2(L + W) × H
Step 2: Deduct Openings
| Opening | Area |
|---|---|
| Standard door | 1.9 m² |
| Window | 1.5 m² |
Step 3: Coverage Rates
| Type | m²/L |
|---|---|
| Interior latex | 10–12 |
| Exterior | 8–10 |
| Primer | 8–10 |
Step 4: Coats & Waste
Most walls need 2 coats. Add 5–10% waste factor.
Worked Example
Room 5×4 m, height 2.5 m, 1 door, 2 windows:
- Perimeter = 18 m
- Gross area = 45 m²
- Deductions = 4.9 m²
- Net = 40.1 m²
- ×2 coats = 80.2 m²
- ÷10 m²/L = 8 L
- +10% = ~9 L
Common Mistakes
- Forgetting to deduct openings
- Using only 1 coat
- Ignoring waste factor
Related
Paint Calculator | Room SA | Rectangle Area | Square Footage | Painting Rooms Guide | Measure Square Footage