Paint Calculator
Work out how much paint you need from wall size, number of coats and the coverage on the tin.
Calculator
Enter the wall area you are covering. Optionally subtract doors and windows, then set coats and coverage.
Paint inputs
Results
Suggested tins use standard UK sizes (1L, 2.5L, 5L and 10L), choosing the fewest tins that meet or slightly exceed the litres required. Porous or dark surfaces may need more product than the tin suggests.
How This Calculator Works
What it does
This calculator estimates how much paint you'll need to cover interior walls based on the wall dimensions, the number of coats, and the paint's coverage rate.
How the calculation works
The total wall area is calculated by multiplying the wall width by the wall height. Door and window areas are then subtracted to determine the net paintable area. The net paintable area is multiplied by the number of coats and divided by the paint coverage (m² per litre) to estimate the amount of paint required.
Formula
- Wall Area = Width × Height
- Net Paintable Area = Wall Area − Door & Window Areas
- Total Paint Area = Net Paintable Area × Number of Coats
- Paint Required (Litres) = Total Paint Area ÷ Coverage per Litre
Why it matters
Estimating your paint requirements accurately helps reduce waste, avoid unnecessary costs and minimise the risk of running out mid-job. Buying enough paint from the same batch also helps maintain a consistent colour and finish throughout the project.
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Frequently asked questions
Straight answers about this calculator and how UK trades use the figures day to day.
What coverage should I use?
Use the figure on the tin or data sheet. Many emulsions quote around 10 to 14 m² per litre depending on surface.
Do ceilings work the same way?
Yes. Enter ceiling length and width as width and height, with doors and windows at zero.
Why exclude doors and windows?
They are not painted with wall emulsion. Subtracting them avoids over-ordering.
How are tin sizes chosen?
The calculator suggests a mix of 1L, 2.5L, 5L and 10L tins that covers the litres required using as few tins as possible.
Does primer count as a coat?
If you are using primer or mist coat, include it in the number of coats or run the calculator twice.
Can I estimate a whole room?
Add the widths of each wall together for total width, keep the room height, and subtract openings once.
Materials Estimated. Job Still To Run.
Keep painting jobs, customer messages and invoices together in Total Tradesmen.
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