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Loan Calculator
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Paint Calculator
Works out how many litres of paint a room needs from its dimensions, deducting doors and windows and allowing for the number of coats.
Calculators
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Free, unlimited
Enter your figures and press Calculate.
In short
Paint Calculator is a free online tool on inputtesthub.com that works out how many litres of paint a room needs from its dimensions, deducting doors and windows and allowing for the number of coats. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.
How to use the Paint Calculator
- Enter your figures in the input fields.
- The result updates as you type, together with the full working.
- Check the breakdown table to see exactly how the number was reached.
About the Paint Calculator
The Paint Calculator works out how many litres of paint a room needs from its dimensions, deducting doors and windows and allowing for the number of coats. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.
What people use it for
- Buying the right number of tins in one trip.
- Checking a decorator’s quantity before agreeing to it.
- Working out whether one tin will finish a feature wall.
Details
| Typical coverage | 11 m² per litre per coat on smooth painted plaster |
|---|---|
| Bare plaster | Can drop to 6–8 m² per litre |
| Standard tin sizes | 1 L, 2.5 L, 5 L, 10 L |
| Doors deducted at | 1.9 m² each |
| Windows deducted at | 1.5 m² each |
The maths behind it
This tool uses Paintable area = perimeter × wall height − openings. Litres = area × coats ÷ coverage rate, plus 5% wastage. A door is counted as 1.9 m² and a window as 1.5 m². Every intermediate value is shown on screen, so the result can be checked by hand.
Coverage is printed on the tin and varies more than any other input here. Bare plaster, textured render and dark-over-light all use far more than the default. Change the coverage field to the figure on the tin you are buying.
Frequently asked questions
How much paint do I need for a 12 × 12 room?
At 2.7 m walls that is roughly 130 m² of wall before openings, so about 24 litres for two coats at 11 m²/L. Enter your own dimensions above — the deduction for doors and windows makes a real difference in a small room.
Why does my tin say a different coverage?
Because coverage depends on the paint and the surface, not just the paint. Emulsion on smooth painted plaster reaches 11–13 m²/L; the same paint on bare plaster or textured wall can halve that as the surface absorbs the first coat.
Should I deduct doors and windows?
Yes, and this tool does. On a small room with a big window, not deducting can overstate the paint by a fifth. What you should not deduct is skirting and architrave — you cut in around them and use the paint anyway.
Do I need an account to use the Paint Calculator?
No charge and no sign-up. There is no free tier to run out of because there is no paid tier — inputtesthub.com is funded by advertising rather than by metering the page.
Can you see what I put into this page?
No. The Paint Calculator runs entirely in your browser using JavaScript. Your input never reaches inputtesthub.com or any third party — open your browser's Network tab while you use it and you will see no request go out.
Can I check the maths myself?
It uses Paintable area = perimeter × wall height − openings. Litres = area × coats ÷ coverage rate, plus 5% wastage. A door is counted as 1.9 m² and a window as 1.5 m². The full working is printed under the result, so you can follow every step rather than trusting a black box.
What is the Paint Calculator used for?
In practice it gets used for three things: buying the right number of tins in one trip. Checking a decorator’s quantity before agreeing to it. Working out whether one tin will finish a feature wall. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Any caveats I should know about?
Coverage is printed on the tin and varies more than any other input here. Bare plaster, textured render and dark-over-light all use far more than the default. Change the coverage field to the figure on the tin you are buying.
What are the reference figures here?
Typical coverage is 11 m² per litre per coat on smooth painted plaster. Bare plaster is Can drop to 6–8 m² per litre. Standard tin sizes is 1 L, 2.5 L, 5 L, 10 L. These are printed on the page itself, so you do not have to take them on trust.
Is the number rounded?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.
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