Paint Calculator

Estimate how much paint a room needs. The calculator works out the wall area, removes doors and windows, adds the ceiling if you want, and divides by the coverage printed on the can.

Measure in
Paint the ceiling too?
Check the can; interior emulsions are often 80 to 140 sq ft per litre.
Results update as you type.

Paint needed

10.2 litres

for 2 coats

Area to paint
507 sq ft (47.1 m²)
Primer (one coat, same coverage)
5.1 litres
Putty (approx.)
26 kgabout 1 kg per 20 sq ft for two coats

Each door is taken as 1.9 m² and each window as 1.5 m². Rough or new walls absorb more paint.

About this calculator

It also estimates primer and wall putty.

How to use it

  1. Enter the room size and height.
  2. Enter doors, windows and whether to paint the ceiling.
  3. Enter coats and coverage.

The formula

Litres = area (sq ft) × coats ÷ coverage per litre
coverage
sq ft per litre per coat, from the can

Worked example

A 12 × 10 ft room, 10 ft high, 1 door, 2 windows, with ceiling

  1. Area = 387 sq ft of walls + 120 sq ft of ceiling = 507 sq ft.
  2. Two coats at 100 sq ft per litre: 10.2 litres.
  3. About 5.1 litres of primer and 26 kg of putty.

What the result means

Buy slightly more and keep the rest for touch-ups.

Assumptions

  • Doors 1.9 m², windows 1.5 m².

Limitations

  • Absorbent or textured walls need more.

Frequently asked questions

How much paint for a 10 × 12 room?

About 10 litres for walls and ceiling in two coats.

How many coats?

Two coats of finish over one of primer is usual.

What is coverage?

The area one litre covers in one coat; it is on the can.

Last reviewed on 3 October 2026. Found a mistake? Tell us.