Home & Garden
Paint calculator
Calculate how much paint you need for a room using dimensions, coats, openings, coverage, and can size.
- Calculates wall and paintable area
- Supports metric and imperial room dimensions
- Rounds cans and estimates leftover
Formula and method
Paint needed formula
wall area = 2 × (length + width) × height; paint = area × coats ÷ coverageThe calculator subtracts doors and windows from the wall area, multiplies by coats, then adds the waste buffer.
Cans are rounded up to whole cans because partial cans are not normally sold.
Assumptions
- Room is treated as a rectangle.
- Openings are subtracted manually.
- Coverage comes from the paint label before surface texture and waste.
Practical examples
Bedroom repaint
5 m × 4 m × 2.7 m, two coats, 10 m²/L
About 11 liters before can roundingSmall office
12 ft × 10 ft × 8 ft, one coat, openings removed
Use the ft²/gallon coverage modeFAQ
Should ceilings be included?
This calculator focuses on walls. Add ceiling area manually as a separate wall-like area if needed.
How much buffer should I use?
5-15% is common depending on surface texture, color change, and touch-up needs.
Can I subtract windows?
Yes. Add the total door and window area in the openings field.
Does primer count as a coat?
If primer is a separate product, calculate it separately with its own coverage.