Paint calculator: litres, tins and mist coat
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
Work out how many litres of paint a room or an outside wall needs, and which mix of tins leaves the least over. There's a mist coat mode for new plaster. Enter your measurements below; every figure we start from is shown and you can change it.
Worked example
| You enter | Value |
|---|---|
| What are you painting? | Walls and ceilings |
| Area to paint | Room: room walls 4 m × 3 m × 2.4 m, less 0.8 × 2 m, 1.2 × 1.1 m |
| Coats | 2 |
| Coverage per coat | 12 m²/L |
| Waste allowance | 10% |
| Tin sizes you can buy | 1, 2.5, 5, 10 L |
Buy: 1 × 5 L + 1 × 1 L
| Result | Value |
|---|---|
| Paint needed | 5.62 L |
| Least left over | 1 × 5 L + 1 × 1 L |
| Fewest tins | 1 × 5 L + 1 × 1 L |
| Area to paint (after openings) | 30.68 m² |
Show the working
- Area: Room 33.6 m² less 2.92 m² openings = 30.68 m²
- Litres: 30.68 m² × 2 coats ÷ 12 m²/L × 1.1 (10% waste) = 5.62 L
- Least left over: 1 × 5 L + 1 × 1 L = 6 L (0.38 L spare)
- Fewest tins: 1 × 5 L + 1 × 1 L = 6 L (0.38 L spare)
How it works
- Net area (m²) = walls (perimeter × height) and ceilings, less doors and windows
- Litres = net area × coats ÷ coverage (m²/L per coat) × (1 + waste)
- Mist coat: paint before thinning = thinned mix ÷ (1 + water parts); water = thinned mix − paint
- Tins: the mix of tin sizes with the least left over (ties go to fewer tins), and the fewest-tins alternative
A maker's coverage figure is a best case on a smooth, sealed surface. Fresh plaster, rough walls and strong colour changes use more.
Masonry paint coverage varies a lot with the surface: smooth render takes far less than pebbledash or brick. Use the figure on the tin for your surface.
Mist coat: a thinned first coat that seals new plaster. Thin it as the maker says, then follow with full coats (switch back to Walls and ceilings). Our guide to painting new plaster explains why.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Coverage per coat: Walls and ceilings | 12 m2/L Sources range 12–17 m2/L | Typical value Not yet checked against the source | BuildBatch's typical emulsion coverage per coat (checked 19 October 2026) Makers state up to 14 (Dulux Matt, via masseys-diy.co.uk) and up to 16–17 (Dulux Trade, via buildbatch.co.uk). A maker's figure is a best case on a sealed surface. |
| Coats: Walls and ceilings | 2 coats | Our assumption Not yet checked against the source | Our choice: change it to suit your job Two coats is our starting point; new plaster or a colour change may need more. |
| Coverage per coat: Masonry paint (outside walls) | Enter from the bag, pack or tin | Typical value Not yet checked against the source | From your product brief v2 §2 (paint: masonry paint mode). Coverage per coat for masonry paint; depends heavily on the surface (smooth render vs pebbledash). Researcher to source from makers' data sheets; until then the user enters the figure from the tin. |
| Coverage per coat: Mist coat (new plaster) | Enter from the bag, pack or tin | Typical value Not yet checked against the source | From your product brief v2 §2 (paint: mist coat mode). Coverage of a thinned mist coat on new plaster. Researcher to source from makers' mist-coat instructions; until then the user enters the figure from the tin. |
| Waste allowance | 10 % | Our assumption Not yet checked against the source | Our choice: change it to suit your job Allowance for rollers, trays and touch-ups. |
| Tin sizes you can buy | 1, 2.5, 5, 10 L | Common UK size Not yet checked against the source | From your product Common UK tin sizes; not every paint comes in every size. |
FAQs
Guides
How much paint do I need for a room?
Measure your walls, take off doors and windows, then work out litres and tins for two coats. Why real coverage is lower than the tin says.
Painting new plaster: mist coats and how much paint
Why fresh plaster soaks up paint, how long to leave it (follow the maker), what a mist coat is and how it changes how much paint to buy.