RoomKitHow it works
Measure each wall using the room perimeter and wall height. Subtract the total surface area of doors and windows that will not be painted. Include the ceiling only if it uses the same product, coverage and number of coats. Divide the coated area by the coverage printed on your paint label, then apply your chosen allowance. Round up to whole containers. Primer, trim, paint for doors and differently colored surfaces need separate estimates.
Formula
Wall area = 2 × (length + width) × height − doors − windows. Litres needed = paintable area × coats ÷ coverage × (1 + allowance/100). Cans = round up (litres ÷ can size).
Example
A 4 × 3 m room with 2.8 m walls, 1.8 m² of doors and 1.5 m² of windows has 35.9 m² of net walls. Two coats at 10 m²/L with 10% allowance need 7.898 L. Buy four 2.5 L cans: 10 L purchased, costing 100 at 25 per can. The reserve is illustrative; rough or absorbent surfaces may need more paint.
Assumptions and limitations
Use the coverage and pack size printed on your product label. Output estimates, not a cutting or installation plan. Materials only. Labor, delivery, tax, primer, adhesive and underlay are excluded.
Sources and assumptions
BEHR · Paint · The Home Depot · Material calculators
Frequently asked questions
Are my measurements uploaded?
No. Your room measurements, product settings, units and currency are stored in this browser. Clear this site’s data to remove them.
Does changing units change the room?
No. Dimensions stay in metres internally. Metric and imperial views convert lengths, areas, litres and US gallons without changing the stored room.
Are the coverage and waste defaults guaranteed?
No. Defaults are examples. Use your product label and adjust for the surface, layout, cuts and installation instructions.