UK home improvement calculator
Paint Calculator UK
Estimate how much paint you may need for walls, ceilings, or both with simple room measurements and editable UK-friendly coverage.
Last reviewed: 25 April 2026
Calculator inputs
Choose the surfaces, enter the room size, then adjust coats and coverage if your paint tin says something different.
Result Card
Estimated paint needed
This estimate is for walls and the ceiling, using 2 coat(s) at 10 m2 per litre.
3.1 m2 has been subtracted for 1 door(s) and 1 window(s).
42.5 m2 x 2 coat(s)
8.5L before the extra 10% allowance
1 x 10L
Useful for touch-ups and small future repairs
Using the coverage shown on your actual paint tin can help avoid buying too much or too little paint.
Fresh plaster, porous walls, dark colour changes and different brands can all change how far a litre really goes.
How this estimate works
See the exact steps behind the estimate so the result stays easy to sense-check.
This calculator estimates the paintable area of your room, subtracts doors and windows, multiplies by the number of coats and divides by the paint coverage per litre. The result is an estimate because coverage can vary by paint brand, surface condition, colour change and application method.
- Wall area = 2 x (room length + room width) x room height
- Ceiling area = room length x room width
- Opening deduction = doors x 1.6 + windows x 1.5, unless you enter a custom opening area
- Total coated area = paintable area x coats
- Litres needed = total coated area / coverage
Coverage note: many UK DIY calculators use around 10 m2 per litre as a safe estimate, but paint tins may show different coverage.
Example calculation
A worked example helps the user compare the result with a familiar everyday scenario.
A 4m x 3m room with a 2.4m ceiling has about 33.6 m2 of walls and 12 m2 of ceiling.
After subtracting 3.1 m2 for one door and one window, painting walls and ceiling with 2 coats at 10 m2/L needs about 9.35L including the extra 10% allowance.
That rounds to a practical recommendation of 1 x 10L.
Simple ways to avoid wasting paint
A few simple checks can make the estimate more accurate and reduce unnecessary tins.
- Measure walls before buying paint.
- Subtract large doors and windows.
- Check the coverage on the paint tin.
- Add a small extra amount for touch-ups.
- Use the right primer on very dark or porous surfaces.
- Keep leftover paint labelled for future repairs.
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Paint calculator questions
Short answers to common paint estimate questions.
How much paint do I need for one room?
It depends on the wall and ceiling area, how many coats you need, the paint coverage per litre and how much area doors and windows remove.
Why is 10 m2 per litre used as the default?
It is a cautious UK DIY starting point that helps avoid underestimating paint. Many tins show around 10 to 13 m2 per litre, but the exact figure can vary.
Should I subtract doors and windows?
Yes for wall painting, especially if the openings are large. Ceiling-only estimates do not need that deduction.
Why add a little extra paint?
A small allowance helps with touch-ups, awkward edges, absorbent surfaces and minor measuring differences.
Estimate notice
This is an estimate. Actual paint needed can vary depending on the product, surface condition, colour change, preparation, and how the paint is applied.