How much paint do I need?
Enter the area you're painting and we'll work out the litres, tins and cost — and show you exactly how we got there, so you can check the maths and buy the right number of tins.
Tip: a wall is roughly length × height. A 4 m × 2.4 m wall ≈ 9.6 m².
| Emulsion paint | 1 × 5 L tin | £28 |
| Rollers, brushes, tape & dust sheets | 1 set | £25 |
- 1Area to paint: 30 m²
- 2Coats: 2 coats
- 3Coverage: 12 m² per litre, per coat (previously painted)
- 4Paint needed: 30 m² × 2 coats ÷ 12 = 5 litres
- 5Tins: 1 × 5 L tin
- Emulsion covers ~12 m²/L per coat on previously painted surfaces.
- Excludes a separate primer/undercoat to bare timber or stains.
How to work out paint quantity
- 1Measure the area
Wall area = length × height for each wall; add them up. A typical wall is 4 m × 2.4 m ≈ 9.6 m². Subtract big openings (a door ≈ 1.5 m², a window ≈ 1.4 m²).
- 2Decide the coats
Two coats is standard. Strong colour changes or bare plaster may need three (after a mist coat).
- 3Divide by coverage
Emulsion covers about 12 m² per litre per coat on previously painted walls, but only ~10 m²/L on new plaster, which is more absorbent.
- 4Round up to tins
Litres needed = area × coats ÷ coverage. Round up to whole 5 L or 2.5 L tins — it's worth having a little spare for touch-ups.
Most paint over- or under-buying comes from guessing the area or forgetting that bare plaster drinks paint. The formula is simple — area × coats ÷ coverage — and the calculator above does it for you and prints every step, so you're not taking a number on faith. That “show the working” approach runs through everything in ScopeWise: when we put a plastering or painting figure in your schedule of works, you can see exactly how many bags or litres it assumes.
Paint coverage quick reference
| Surface | Coverage per litre | Notes |
|---|---|---|
| Previously painted (smooth) | ~12 m² / coat | Standard matt emulsion |
| New / bare plaster | ~10 m² / coat | More absorbent — mist coat first |
| Textured / heavily prepped | ~8–10 m² / coat | Use the lower figure |
| 5 L tin (2 coats) | ~30 m² | Covers a small room's walls |
Indicative — always check the tin's stated coverage.
Frequently asked questions
How much paint do I need for one room?+
For an average double bedroom (walls ~30 m² after openings), two coats of emulsion needs roughly 5 litres — a single 5 L tin. Add the ceiling (~12 m²) and you'd want a little more. Use the calculator above for your exact dimensions.
How many square metres does a litre of paint cover?+
Around 12 m² per litre per coat on a smooth, previously painted surface, dropping to about 10 m²/L on new plaster and less on textured walls. Two coats roughly halves the area a litre covers.
Do I need a mist coat on new plaster?+
Yes. New plaster should get a 'mist coat' first — emulsion thinned with water (around 3:1) — to seal it, before your two top coats. The calculator's 'new plaster' option uses the higher paint requirement.
Should I buy extra?+
A little. Buying one consistent batch avoids slight colour variation, and you'll want some left for touch-ups. Rounding up to the next tin usually covers this.
Related tools & guides
Want to know how these figures are calculated? See our cost methodology.
Cost figures shown are indicative estimates, not quotations. You are responsible for verifying all costs (obtain contractor quotes) and any figures submitted to a lender. ScopeWise is a documentation tool, not financial, tax, structural or planning advice. HMO compliance prompts are guidance only — confirm requirements with your local council, as standards and licensing vary by authority.