Paint calculator
Buying paint by eye usually ends in one of two ways: a second trip to the store halfway through the last wall, or several half-full tins in the garage. The calculation behind it is simple — wall area, minus what you don't paint, multiplied by the number of coats and divided by the coverage — and this calculator does it for you.
Enter the room's dimensions, the area of doors and windows, and the coverage from the label of the paint you're considering. Switch to imperial units if you work in feet and gallons.
Your measurements
Printed on the tin — usually 8–14 m²/L for interior emulsion.
Result
- Wall area (one coat)
- 33.40 m²
- Total area to cover
- 66.80 m²
- Paint needed
- 6.7 L
Real coverage varies by brand and by surface — check the label of the paint you choose.
How the calculation works
- Room perimeter = 2 × (length + width).
- Wall area = perimeter × wall height, minus the area of doors and windows.
- Area to cover = wall area × number of coats.
- Paint needed = area to cover ÷ coverage (the area one litre covers in one coat). If you enter a tin size, the number of tins is rounded up.
Worked example
A 4 × 3 m room with 2.6 m walls has a perimeter of 14 m and 14 × 2.6 = 36.4 m² of wall. Deduct 3 m² for a door and a window and 33.4 m² remain. Two coats mean 66.8 m² to cover; at 10 m² per litre you need 6.7 litres — in practice one 10-litre tin, or a 5-litre and a 2.5-litre tin.
What the calculator assumes
- Interior emulsion typically covers 8–14 m² per litre per coat (roughly 325–570 ft² per US gallon); the exact figure is on the tin and depends on the product.
- The ceiling is not included. If you paint it too, add length × width to the area.
- Two coats are the norm for an even finish. A third coat is often needed when going from a dark colour to a light one.
When to adjust the result
- New plaster or fresh filler absorbs much more of the first coat — apply a primer or a mist coat first, otherwise consumption rises.
- Rough surfaces (textured plaster, bare blockwork) use noticeably more paint than the label suggests.
- Paint for woodwork, metal or radiators has a different coverage; use the figure from that product's label.
Frequently asked questions
How much paint do I need for a 4 × 3 m room?
With 2.6 m walls, about 3 m² of doors and windows and two coats, around 6.7 litres of paint at a coverage of 10 m² per litre. A paint with lower coverage, or a third coat, increases that amount.
Should I deduct doors and windows?
Yes, for large openings such as doors, windows and fitted wardrobes. Small items like sockets and switches are not worth deducting — the difference is covered by the paint lost in the tray and on the roller.
Does a primer coat count as a coat of paint?
No. Primer is a separate product with its own coverage. Calculate it separately, using the coverage of the primer, and then the number of top coats here.