Paint Coverage Calculator
Buying paint goes wrong in two directions. Measure the walls and forget the doors and windows, and you buy too much; forget that two coats means painting the room twice, and you buy too little and have to match a batch later. This does both steps, and rounds tins up rather than to the nearest — because three-quarters of a tin does not exist in a shop.
What this generator does
Adds up the wall areas, subtracts a standard door and window area for each opening, multiplies by the number of coats, and divides by the paint's coverage rate — then rounds up to whole tins.
How to use this tool
- Set how many walls and how many coats.
- Read the wall area, then what the doors and windows take off.
- Check the total painting figure — that is the area times the coats.
- Buy the tins shown; the calculation rounds up so you are not left short.
Understanding the controls
- How many walls
- Between 1 and 6 walls, each generated with a plausible width and a ceiling height between 2.2 and 3 metres.
- How many coats
- Two is usual. Bare plaster drinks the first coat, and a strong colour over a pale one may need three.
- Seed
- Any word reproduces exactly the same room and the same answer.
Common use cases
- Working out paint for a room before going to the shop
- Checking a decorator's quantity estimate
- Understanding why two coats is not the same as one big one
- Teaching area calculation with something people actually do
- Setting the same room twice from a seed
How this generator works
A standard door is treated as just under two square metres and a window as about one and a half. The check does more than recompute: it confirms the tins actually bought, times their size, times the coverage rate, genuinely reach the total area to be painted — so a rounding error can never leave the job short.
Randomness and fairness
The room dimensions, openings and coverage rate are generated randomly; the arithmetic on them is exact. A seed reproduces the same room exactly and is therefore explicitly not cryptographically secure. Without a seed the browser's cryptographically secure generator is used.
For how randomness is produced across the whole site, see how Generate Random works.
Limitations and good to know
- Standard door and window sizes are assumed rather than measured — a patio door or bay window will be well out.
- Coverage rates vary by paint and surface. The figure used is typical for emulsion on prepared walls.
- Ceilings, skirting, frames and any second colour are not included.
- Tin sizes are fixed at 2.5 litres, which is the common size but not the only one.
- Rooms are not stored between visits; seed one you want again.
Privacy and your data
Every figure is worked out on your own device. Neither the room nor your seed leaves the browser.
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