Paint calculator
Paint quantity is area divided by spreading rate, times coats. The spreading rate is on the tin and varies a lot.
m2 per litre
Paint needed
9.70L
- 5 litre tins
- 2
- In US gallons
- 2.562
- Area to paint
- 58.20
- Area including all coats
- 116.40
- Paint per coat
- 4.85
Show the working
- Room length = 5
- Room width = 4
- Wall height = 2.4
- Door and window area = 5
- Coats = 2
- Spreading rate = 12
- Include the ceiling = 1
- wall_area = 2 * (5 + 4) * 2.4 = 43.2
- ceiling_area = 1 > 0 ? 5 * 4 : 0 = 20
- Area to paint = max(43.2 + 20 - 5, 0) = 58.2
- Area including all coats = 58.2 * 2 = 116.4
- Paint needed = 116.4 / 12 = 9.7
- 5 litre tins = ceil(9.7 / 5) = 2
- In US gallons = 9.7 / 3.785411784 = 2.562 47
- Paint per coat = 58.2 / 12 = 4.85
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- litres = (area - openings) x coats / spreading rate
Spreading rates on the tin assume a smooth, sealed, previously painted surface. Bare plaster, textured walls and dark-to-light changes all take more.
The first coat on new plaster is a mist coat and covers much further than the tin claims.