Paint calculator
Work out how much paint a room needs from its dimensions, the surfaces to paint, door and window openings, coverage per liter and the number of coats — including 1 L, 5 L and 18 L pack counts.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
Room and paint
Wall area = 2 × (length + width) × height, ceiling area = length × width. Openings are subtracted, then the coats and the wastage allowance are applied.
Paint needed
50.40 m²
20.00 m²
6.40 m²
64.00 m²
128.00 m²
13.44 L
1 L × 14 tins (leftover 0.56 L)
5 L × 3 tins (leftover 1.56 L)
18 L × 1 tins (leftover 4.56 L)
What this tool does
- Buy the right number of tins before you start: enter the room size and coats to get the liters needed and the 1 L / 5 L / 18 L pack counts.
- Unsure how much the doors and windows save? Enter the counts and the tool subtracts them from the wall area automatically.
- See how much extra a third coat costs by changing the coat count and comparing the liters.
- Check the paint quantity on a decorator’s or shop’s quote so you are not charged for extra tins.
Example
Input
Room 5 × 4 × 2.8 m, walls and ceiling, 1 door (1.9 m²), 2 windows (2.25 m² each), coverage 10 m²/L, 2 coats, 5% wastage
Output
Walls 50.40 m², ceiling 20.00 m², openings 6.40 m², paintable area 64.00 m², total painted area 128.00 m², paint needed 13.44 L; 18 L × 1 tin (leftover 4.56 L), 5 L × 3 tins (leftover 1.56 L), 1 L × 14 tins (leftover 0.56 L)
The area is “four walls + ceiling − openings”, and both the coats and the wastage multiply the liters, so 64 m² over two coats becomes 128 m².
Frequently asked questions
What coverage figure should I use?
Use the “per liter, one coat” number on the tin — emulsion paint is usually 10–12 m²/L, a little higher for primer and lower for strong colours. For poor coverage or a repaint over a dark colour, estimate conservatively at 8–10 m²/L.
Should doors and windows be deducted?
Yes, but you do not need millimetre accuracy. A typical door is about 1.9 m² (0.9 × 2.1 m) and a window about 2.25 m² (1.5 × 1.5 m), so entering the counts is enough. If the openings are small, or you are also painting frames, keeping a little spare is safer.
How much wastage should I allow?
About 5% for roller application; up to 10% for spraying, rough surfaces or a light colour over a dark one. Wastage is applied to the liters, and you buy whole tins rounded up, so err on the generous side.
Why are the tins rounded up?
Paint is sold by the tin, so 13.44 L means three 5 L tins. The tool shows the count and the leftover for each pack size so you can pick the packaging that fits your budget and colour plan.
Does a third coat really need a third of the paint?
Not quite. Second and third coats usually use less paint because the surface is already sealed. The tool multiplies linearly, which is a conservative estimate — real usage tends to come in slightly under the result.
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