How much paint do I need? Working out wall paint properly

Too little paint means a second trip to the DIY shop, and maybe a slightly different shade from a new batch. Too much means half-full tins in the shed that have dried out two years later. With a simple formula you buy exactly the right amount, whether you're painting one room yourself or pricing a whole flat as a decorator.

The formula

Paint in litres = area to paint (m²) × number of coats ÷ coverage (m²/l)

Then: round up to full tins.

So you need three values: the area, the number of coats and the coverage of the specific paint.

Step 1: Work out the area to paint

Walls: room perimeter × room height. Perimeter: (length + width) × 2. Deduct: windows and doors (width × height × number). Ceiling: length × width (= floor area).

Example: bedroom 4.0 × 3.5 m, height 2.6 m, one door 0.9 × 2.0 m, one window 1.2 × 1.4 m.

• Perimeter: (4.0 + 3.5) × 2 = 15.0 m
• Walls gross: 15.0 × 2.6 = 39.0 m²
• Deductions: door 1.8 m² + window 1.68 m² = 3.48 m²
• Walls net: 35.5 m²
• Ceiling: 14.0 m²

Tip for professionals: In Germany, painters' billing rules (VOB, DIN 18363) often don't deduct small openings up to 2.5 m²; for purchasing, deduct them anyway, so you don't buy too much. Window and door reveals, on the other hand, should be added if they are being painted.

Step 2: Number of coats

If in doubt, allow for two coats. One coat is usually "enough" only on the tin.

Step 3: Coverage: it's on the tin

The coverage (m² per litre per coat) is given on the tin or in the technical data sheet. For interior wall paints, typical figures are roughly between 6 and 8 m²/l, and cheap paints often cover worse than the number promises.

Look at the opacity class under EN 13300 (class 1 = best opacity), and at the coverage it's stated for. "Class 2 at 7 m²/l" means: if you spread it thinner, you won't achieve that opacity.

Rough surfaces (woodchip, textured plaster) use more. Add 10–20% there.

Step 4: Do the maths

Example with 7 m²/l, 2 coats:

• Walls: 35.5 × 2 ÷ 7 = 10.1 l
• Ceiling (white ceiling paint, 7 m²/l, 2 coats): 14.0 × 2 ÷ 7 = 4.0 l

Step 5: Round up to full tins and combine cleverly

Paint often comes in 1 / 2.5 / 5 / 10 litres. For 10.1 l of wall paint:

Which combination is cheapest depends on the prices: the 10 l tin is often noticeably cheaper per litre. For colours mixed in the shop's tinting machine: have it all mixed at once, or you risk differences in shade.

Quick table: litres of wall paint per room

(2 coats, 7 m²/l, room height 2.5 m, 1 door, 1 window, walls only)

For guidance only: calculate with your real measurements and the coverage of your paint.

Common mistakes

1. Reading coverage "per tin" instead of per coat.
2. Not deducting windows and doors: with large glazed walls, that's easily 10–15% too much.
3. Forgetting the ceiling, or calculating it with wall paint.
4. Forgetting primer on new plaster or plasterboard.
5. Buying more paint later from several batches: visible joins.

Online calculator, Excel or an app?

Manufacturers' online paint calculators are free and good for a single room. For a whole flat, though, you type in every room again, and you rarely get a shopping list. Excel works if you build yourself a template once.

An app is worth it if you have several rooms or jobs and measure on site: each room entered once, all materials on one list.

How we do it ourselves: UZYTAK Materials

In our own renovation company, we didn't want to do the sums on scraps of paper for every flat again. That's why there's UZYTAK Materials:

• Enter the room once: length, width, height, doors and windows with quantities, L-shape, bay windows and alcoves. Wall, floor and ceiling area appear instantly.
• Paint calculator: number of coats, coverage per litre, tin sizes (1 / 2.5 / 5 / 10 l, editable). The app picks the cheapest tin combination using your prices, or, without prices, the one with the least left over.
• More calculators: tiles, laminate, plasterboard, plaster and filler, skirting boards, with results always in full packs.
• One shopping list for all the rooms in a job; identical materials are combined and rounded only once.

Price: free for 1 project with unlimited rooms and all calculators, no ads and no account. Pro one-off €9.99: unlimited projects, shopping list as a PDF with prices and totals. No subscription, your data stays on your phone.

To be honest: all results are estimates. You set the coverage as stated on your tin. Metric units only.

Frequently asked questions

How much paint for 10 m² of wall? At 7 m²/l and two coats: 10 × 2 ÷ 7 ≈ 2.9 l, so a 2.5 l tin plus a little more; in practice a 5 l tin or 2.5 + 1 l.

How much paint for a 60 m² flat? As a rough guide: wall area ≈ 2.5–3 × floor area. For 60 m² that's about 150–180 m² of wall, which with two coats and 7 m²/l comes to about 43–51 l, plus ceilings. For buying, though, calculate room by room.

Do I need primer? On new plaster, plasterboard or highly absorbent surfaces, usually yes; see the paint's data sheet.