How to use this calculator
Estimate how much paint a room needs after subtracting typical door and window areas.
How the calculation works
- Calculates total wall area from room perimeter and wall height.
- Subtracts estimated door and window areas.
- Multiplies by the number of coats and divides by paint coverage per unit.
Formula
Paint needed = ((2 x (length + width) x height - openings) x coats) / coverage per unit.
Example
A 4 m by 3 m room with 2.6 m walls, one door, two windows, two coats, and 10 m² per liter needs about 5 liters.
Understanding your result
Use the paint estimate as a buying guide, then round up for surface texture, waste, primer needs, and touch-ups.
Assumptions and limitations
- Surface texture, primer, application method, paint product, and waste can affect actual usage.
- Round up before buying paint so you have enough for touch-ups.
Frequently asked questions
Should I buy exactly this amount?
Usually no. Round up so you have enough for waste, texture, mistakes, and touch-ups.
Are doors and windows exact?
No. The calculator subtracts typical opening areas, so unusual openings may need manual adjustment.