The calculation
Paint volume = coated area ÷ coverage
Paintable area × coats ÷ product coverage × (1 + allowance)
- Room wall area is 2 × (length + width) × wall height.
- Doors and windows are deducted before coats and coverage are applied.
- The exact volume is rounded up to whole selected cans or pails for the purchase estimate.
- Use separate estimates when walls, ceilings, primer, or trim use different products.