Paint Calculator

Paint is costly, and running short in the middle of a job can leave patches that don't match. This calculator estimates the litres of paint for a room from its size, the doors and windows, the number of coats and the coverage printed on the paint can.

How to use the paint calculator

1. Enter the room length, width and wall height in feet.
2. Enter the number of doors and windows.
3. Choose whether to paint the ceiling too.
4. Enter the number of coats (usually 2) and the coverage per litre per coat from the paint can.
5. Enter the price per litre to see the cost.

How it is calculated

Wall area   = 2 × (length + width) × height − doors × 21 sq ft − windows × 15 sq ft
Paint area  = wall area + ceiling area (length × width), if chosen
Litres      = paint area × coats ÷ coverage per litre per coat

A door is taken as 3 × 7 ft and a window as 3 × 5 ft. Many interior emulsions cover roughly 100 to 150 sq ft per litre per coat on a smooth, primed wall, but this varies a lot by brand and surface, so always use the figure on your can.

Example

A room 12 × 10 ft with 10 ft walls, 1 door, 2 windows, the ceiling included, 2 coats, coverage 120 sq ft per litre and paint at ₹300 a litre:

• Walls: 2 × (12 + 10) × 10 − 21 − 30 = 389 sq ft
• Plus ceiling: 389 + 120 = 509 sq ft
• Paint: 509 × 2 ÷ 120 = 8.5 litres, so buy 9 litres
• Cost: about ₹2,545

Tips

• New walls need putty and primer before paint. These are extra and have their own coverage.
• Rough or porous walls drink more paint. Keep 10% extra.
• Buy all cans of one shade together and mix them in a bucket so the colour is even.