Interior wall calculator
Room paint calculator
Estimate paint for the four walls of one rectangular room. Enter room dimensions, opening counts, coats, product coverage, and waste.
Interior paint estimator
Enter room details
Estimates cover the four walls only.
Estimated requirement
Paint needed
For 2 coats on the paintable wall area.
- Gross wall area
- 33.6 m²
- Door deductions
- 1.9 m²
- Window deductions
- 3.0 m²
- Paintable wall area
- 28.7 m²
- Area across all coats
- 57.4 m²
- Waste paint added
- 0.6 L
- Secondary equivalent
- 1.7 gal
- Coverage / waste
- 10 m²/L / 10%
The estimate excludes ceiling, floor, trim, primer, doors, and window frames.
Narrow scope
Assumptions
- The room is rectangular and only its four walls are painted.
- Each door deducts 1.9 m² and each window deducts 1.5 m².
- Coverage is editable because products, texture, porosity, color, and application vary.
- The estimate excludes ceiling, floor, trim, doors, frames, exterior surfaces, and separate primer.
Opening deductions are nominal; packaging and can quantities are intentionally not estimated. See the shared calculation methodology.
Transparent method
Formula and method
Gross wall area = 2 × (length + width) × wall height
Paintable area = gross area − opening deductions
Coated area = paintable area × coats
Paint required = coated area ÷ coverage × (1 + waste ÷ 100)
Verified example
A 4 m × 3 m room with 2.4 m walls
With one door, two windows, two coats, 10 m²/L coverage, and 10% waste, gross wall area is 33.6 m², paintable area is 28.7 m², and the requirement is 6.3 litres or 1.7 US gallons.
Common questions
Paint calculator FAQ
What surfaces are included?
Only the four walls of one rectangular room are included.
How are doors and windows deducted?
The model subtracts 1.9 m² per door and 1.5 m² per window.
Why can I edit coverage?
Coverage varies by paint, texture, porosity, color, and application. Use the product label.
How do coats affect the result?
Paintable wall area is multiplied by the whole-number coat count before coverage and waste.
Why might actual use differ?
Preparation, absorption, application losses, and real opening sizes can change consumption.
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