MetraNestStart with the right area
Add together the walls that will receive the same paint. Subtract doors, windows and areas you are leaving untouched. Calculate the ceiling separately if its paint or coverage rate differs. For a rectangular room, our wall area calculator saves you adding each wall separately.
Use the coverage stated on the tin
A coverage rate of 10 m²/L means one litre covers ten square metres for one coat under the manufacturer’s stated conditions. Two coats double the theoretical requirement. An absorbent or uneven surface may use more: choose an explicit allowance and use the product instructions as your reference.
Read the number of tins
The calculation rounds the final requirement up to a whole tin. This packaging reserve may already be substantial: check it before adding another tin. If comparing different tin sizes, repeat the calculation for each. The best purchase also depends on price and how much you want to keep for touch-ups.
Estimated litres = area × number of coats ÷ coverage rate × (1 + allowance ÷ 100). Tins = estimated litres ÷ tin capacity, rounded up.
One wall and a few touch-ups
For 45 m², two coats, an entered coverage rate of 10 m²/L and a chosen allowance of 10%, the requirement is 9.9 L. With 2.5 L tins, you need four tins, or 10 L purchased. The 10% is an assumption for this example.
Details to check
- Enter the coverage rate of the product you will buy.
- Make a separate calculation for each colour or finish.
- Keep the product reference and colour code with your project sheet.
Frequently asked questions
Is primer included?
No. Calculate it separately using its area, number of coats and its own coverage rate.
Can I use the result for an outdoor surface?
The quantity formula is the same, but coverage rate and application conditions must come from the product intended for that surface.
Method and references · Editorial review: 25 October 2026
The geometric formulas are explained here. For a product, its packaging dimensions and coverage rate remain the reference inputs.