How Much Paint Do I Need? Free Calculator & Guide
Wondering how many litres of paint to buy? Our free calculator gives you an exact answer instantly — just enter your wall dimensions.
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How Much Paint Do I Actually Need?
The short answer: one litre of standard interior paint covers approximately 10–12 m² per coat on smooth walls. For a typical bedroom with around 30 m² of paintable wall area, you'll need approximately 6 litres for two coats. But your exact figure depends on your surface type, number of coats, and the specific paint you choose.
The formula is: (Wall Area × Number of Coats) ÷ Coverage Rate = Litres Required. Use our calculator above to get an instant result — just enter your wall length, height, and number of coats.
Step-by-Step: How to Work Out Paint Quantity
Step 1 – Measure Every Wall
Measure each wall's width and height in metres. Multiply to get the area for each wall, then add them all together. For a 4m × 4m room with 2.4m ceilings: 4 walls × 4m × 2.4m = 38.4 m².
Step 2 – Subtract Doors and Windows
Each standard door is approximately 1.8 m² and each window is about 1.4 m². Subtract these from your total. A room with one door and two windows: 38.4 − 1.8 − 2.8 = 33.8 m².
Step 3 – Apply the Coverage Formula
Divide the net area by your paint's coverage rate (e.g. 10 m²/L), then multiply by number of coats: 33.8 ÷ 10 × 2 = 6.76 litres. Buy 7 litres.
Step 4 – Add a 10% Buffer
Always add around 10% to cover edges, roller waste, and future touch-ups. For 6.76 litres, buy 7–8 litres. Better to have a little left over than run out mid-wall.
Typical Paint Quantities by Room
| Room | Approx Wall Area | Litres Needed (2 coats) | Recommended Tin Size |
|---|---|---|---|
| Small bedroom (3m × 3m) | ~27 m² | ~5.4 litres | 2 × 3L or 1 × 5L + 1L |
| Standard bedroom (3.6m × 3.6m) | ~35 m² | ~7 litres | 1 × 5L + 1 × 2.5L |
| Master bedroom (4m × 4.5m) | ~40 m² | ~8 litres | 2 × 5L |
| Living room (5m × 4m) | ~47 m² | ~9.4 litres | 2 × 5L |
| Kitchen (3m × 3.5m) | ~31 m² (less cabinets) | ~5 litres | 1 × 5L |
| Bathroom (2.5m × 2m) | ~22 m² | ~4.4 litres | 1 × 5L |
Common Mistakes When Buying Paint
Not measuring first — even a rough estimate is far better than guessing by "eye"
Forgetting to multiply by number of coats — one coat almost never gives adequate coverage
Ignoring the surface type — porous and textured surfaces always require more paint
Buying different batch numbers — tins from different batches can have subtle colour differences
No buffer — running out of paint mid-project is more expensive than buying a little extra upfront
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