Paint Calculator
Enter the room length, width and ceiling height, plus doors and windows, to estimate the paintable wall area, the paint litres needed and the cost, accounting for coats and coverage.
Input Data
Results
At a glance:Gross wall area = (length + width) × 2 × height. Deduct the total door and window areas to get the net paintable area. Paint litres = net area × coats ÷ coverage per litre. Cost = litres × price per litre. New or dark-to-light repainting needs more coats; the coverage on rough/porous walls is lower than the can label.
Formula
Gross wall area = (L + W) × 2 × H
Net area = gross − door area − window area
Paint (L) = net area × coats ÷ coverage
Cost = paint × price per litre
$$A_g = (L+W)\cdot 2 H$$$$A_n = A_g - A_d - A_w$$$$V = \frac{A_n\, n}{c}$$$$C = V\, p$$How to Use
- Enter the room length, width and ceiling height (m).
- Enter the number and size of doors and windows.
- Enter the number of coats (commonly 2).
- Enter the coverage per litre (m²/L) from the can.
- To budget, enter the price per litre.
- The tool outputs gross wall area, net area, paint litres and cost.
Case Studies
Bedroom repaint
4×3 m, 2.7 m high, 1 door 2×0.9, 1 window 1.5×1.2.
Gross 37.8 m²; net 33.3 m²; 2 coats at 10 m²/L → about 6.7 L.
Living room with two windows
6×4 m, 2.8 m high, 1 door, 2 windows 1.5×1.2.
Gross 56 m²; net 49.4 m²; 2 coats, 9 m²/L → about 11 L.
FAQ
Why deduct doors and windows?
Those surfaces are not painted, so subtracting them avoids over-buying; but frames and trims use a little, partly offsetting.
How many coats do I need?
New walls commonly 2 coats; covering a dark or vivid colour with light needs 2–3 coats, raise the count accordingly.
Related Tools
References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.