Paint Calculator | How Many Litres of Paint?
Paint calculator: how many litres of paint and primer from room width, length and height? Doors, windows, ceiling, coats, waste and can count.
How is paint quantity calculated?
Quantity depends on net area, number of coats and the one-coat coverage on the can (m²/L). In a rectangular room, wall area is perimeter × height. Doors and windows are subtracted; the ceiling is optional. Waste covers touch-up and leftover in the can, and can count is rounded up.
Steps
- Enter room width, length and wall height. If several identical rooms share the size, enter the room count.
- Enter door and window counts and sizes. Add extra unpainted area (m²) for niches or columns.
- Include the ceiling when it uses the same product.
- Pick a surface or type the m²/L from the label. Interior paint is usually 2 coats; primer is usually 1.
- Set waste (10% is common) and can size. Optional can prices estimate material cost.
Formula
- Wall area: 2 × (width + length) × height × rooms
- Net area: Wall area − doors − windows − extra openings + ceiling
- Paint litres: Net area × coats ÷ coverage × (1 + waste %)
- Primer litres: Net area × primer coats ÷ primer coverage × (1 + waste %)
- Cans: Litres ÷ can size, rounded up
Coverage is for one coat. In area mode, enter gross wall m² directly; ceiling is added and openings are subtracted. For irregular rooms, use an equivalent width and length.
Approximate one-coat coverage
Ranges are a guide for water-based interior and exterior paints. Type the m²/L printed on the can before you buy.
| Surface | Paint (m²/L) | Primer (m²/L) |
|---|---|---|
| Smooth, previously painted wall | 10–14 | 10–12 |
| New plaster or gypsum (absorbent) | 7–10 | 7–9 |
| Textured or rough surface | 5–8 | 6–8 |
| Exterior render | 4–8 | 5–8 |
Practical tips
- A third coat is common when covering a dark colour or stains. Set coats to 3.
- Keep a primer coat on new plaster and bare gypsum. On a sound, similar-colour wall you can set primer coats to 0.
- If the ceiling paint differs from the wall paint, leave the ceiling off and calculate that area separately.
- For exterior work, estimate scaffold with the facade scaffold calculator. Textured render lowers m²/L.
- Cans round up separately: 16 litres in a 15 L can means 2 cans.
Site note
The result is a planning estimate. Absorption, thinning, roller versus spray and colour change all move consumption. Confirm the order against the product label and the surface.
Related calculators
Surface and facade work before paint:
Frequently asked questions
How many square metres does 1 litre of paint cover?
On a smooth, previously painted interior wall, most water-based paints cover about 10–14 m² per litre per coat. New plaster is closer to 7–10 m²/L, and textured exterior render about 4–8 m²/L. The can label is the figure to use. This tool opens at 12 m²/L for a smooth wall.
How many litres of paint does a room need?
Wall area is 2 × (width + length) × height, minus doors and windows, plus the ceiling if you paint it. Litres = net area × coats ÷ (m²/L) × (1 + waste). A 4×5 m room, 2.8 m high, one door, one window, ceiling included, 2 coats at 12 m²/L needs about 12 litres.
How many coats should I apply?
Two finish coats are standard indoors. Primer is usually one coat on new or absorbent surfaces. Moving from a dark colour to a light one may need a third finish coat.
Do I need primer?
Primer helps adhesion on new plaster, gypsum and bare surfaces and steadies finish-coat use. On a sound wall of a similar colour, set primer coats to 0 and estimate finish paint only.
How much waste should I allow?
10% is a common allowance for touch-up, paint left in the can and cutting in at edges. Use 15% on broken-up rooms or dark colours.
How are paint cans rounded?
Litres are divided by can size and rounded up. With a 15 L can, 12 litres is 1 can and 16 litres is 2 cans. Paint and primer round separately.
Is the result a final order quantity?
No. Surface absorption, thinning and application method change use. Entering the coverage from the label brings the estimate closer.