How Much Paint Do You Need? Doors, Windows, Coats and Coverage
Estimate paint from net wall area, coats and actual product coverage. Compare whole tin quantities with a worked room example and explicit allowances.
A useful starting point
Subtract excluded openings from the painted wall area, multiply by coats and divide by the chosen product's coverage. Make allowances explicit and compare whole tins; measure primer, ceilings and other paint systems separately.
Paint quantity starts with the surface you will paint, the number of coats and the selected product's coverage. A “medium room” label cannot replace wall measurements.
Dulux's calculation guide separates these inputs, while its product-based calculator makes the chosen paint relevant. Use the current tin or data sheet rather than a coverage figure from another product.
Measure surfaces and openings
Record each wall's length and painted height. Deduct doors and windows that will not receive this coating. Count the ceiling separately if it is included. Keep woodwork or primer in another estimate when its coating system differs.
Check units before multiplying: a 90 cm doorway is 0.9 m wide. The area of the floor is not the area of the walls.
Work through a room
Our hypothetical room measures 4 × 3 m, with 2.7 m-high walls. Exclude a 0.9 × 2.1 m door and a 1.5 × 1.2 m window; the ceiling is outside this example.
| Quantity | Calculation | Result |
|---|---|---|
| Gross walls | 2 × (4 + 3) × 2.7 | 37.8 m² |
| Openings | 1.89 + 1.8 | 3.69 m² |
| Net walls | 37.8 − 3.69 | 34.11 m² |
| Two coats | 34.11 × 2 | 68.22 m² |
| Paint at assumed 10 m²/L | 68.22 ÷ 10 | 6.822 L |
The example needs 6.822 L before whole-tin rounding. Coverage is an illustrative input, not a guarantee for your surface. The tool has no separate waste field; record any additional planning reserve outside its result. Enter actual coverage and coats in the paint calculator.
Compare whole containers
For the 6.822 L target, buying only one size requires seven 1 L tins, three 2.5 L tins or two 5 L tins. Purchased volumes are 7, 7.5 and 10 L. Compare the prices and useful surplus.
The tool compares uniform sizes separately; it does not optimize a mixed-size order. Check product, base, tint and finish consistency across the tins.
Resolve uncertainty before ordering
Repaired or absorbent walls, a strong colour change and application method can affect the appropriate coating system. Confirm preparation, primer and coats with the manufacturer or decorator. Adding an allowance does not correct a wrong specification.
Keep a note of the coverage assumption and whether it is per coat. Do not multiply a two-coat total by two again, or round each wall's paint upward before combining the surfaces.
Questions before purchase
Can kilograms replace litres?
Not without the density of that product. Container weight and paint volume are different quantities.
Are doors and skirting included?
Only if they receive the same paint and belong in the measured scope. Otherwise estimate them separately. Connect the material order to the renovation budget and use the skirting guide for board quantities.
