Paint Calculator Calculators
How much paint a room needs, allowing for coats, doors and windows.
Paint Calculator is a free online tool that how much paint a room needs, allowing for coats, doors and windows. It runs entirely in your web browser using plain JavaScript, so files are processed on your own device and never uploaded to a server. There is no sign-up, no file size limit imposed by the site, no watermark and no paid tier.
- Price
- Free — no account, no quota, no watermark
- Category
- Calculators
- Where it runs
- In your browser, on your device
- Files uploaded
- None
- Technology
- plain JavaScript
- Settings
- 8
- Works offline
- Yes, after the first visit
About Paint Calculator
Coverage figures printed on a tin assume the best case: a smooth, sealed, previously painted surface, rolled by someone who is not being generous. Bare plaster absorbs the first coat and can halve that number; textured wallpaper, render and masonry are worse. The estimate here uses the figure you give it and subtracts real openings — a standard door is about 1.5 m², a typical domestic window about 1.4 m² — rather than pretending the walls are unbroken.
How to use it
- Enter room width, room length and wall height.
- Adjust the remaining 5 settings if the defaults do not fit your case.
The 8 settings
| Setting | What it does | Default |
|---|---|---|
| Room width | Range 0.5–50m. | 4m |
| Room length | Range 0.5–50m. | 3m |
| Wall height | Range 1–10m. | 2.4m |
| Doors | Range 0–10. | 1 |
| Windows | Range 0–20. | 1 |
| Include the ceiling | On or off. Off by default. | Off |
| Coats | Range 1–5. | 2 |
| Coverage on the tin | Range 1–20m²/L. | 12m²/L |
Under the hood
| Runs on | plain JavaScript — runs the whole thing |
| Controls | Room width, Room length, Wall height, Doors, Windows, Include the ceiling, Coats, Coverage on the tin |
Questions
Do I really need two coats?
Over an existing color of similar tone, usually. Over bare plaster, over a dark color, or with a strong shade, expect three — and prime the plaster first, because a mist coat is far cheaper than a third coat of finish paint.
Why is my actual usage higher than this?
Surface porosity, almost always. A tin claiming 12 m² per liter might manage 6 on new plaster. Texture matters too — a rolled surface has more area than a flat one, and Artex or heavy render can double consumption.
Should I subtract skirting and coving?
Not usually worth it — they are a small share of the wall and the difference is inside the rounding to whole tins. Do subtract a large fireplace, a fitted wardrobe wall or floor-to-ceiling glazing, since those are several square meters each.