Painting
Paint Calculator
Enter your room size and we will tell you how much paint to buy, including the tins to pick up.
Results update as you type. Nothing to sign up for.
Measurements
Switch between metric and imperial at the top of the form.
Floor to ceiling.
Adds the floor area to the area being painted.
Material
Two coats give even colour on most walls.
Printed on the tin. Around 10 m²/L for emulsion.
You need approximately
7.5L
of paint to buy
Area to paint
29m²
Coats
2
Coverage
10m²/L
Waste allowance
10%
Your measurements
- Room perimeter
- 14 m
- Wall area
- 33.6 m²
- Doors and windows deducted
- -4.6 m²1 door, 2 windows
- Area to paint
- 29 m²
How much paint
- Total area over 2 coats
- 58 m²
- Paint needed
- 5.8 L
- With 10% waste
- 6.38 L
- What to buy
- 1 × 5 L + 1 × 2.5 L7.5 L in total
What to buy
Paint
1 × 5 L + 1 × 2.5 L
7.5 L total
Want a cost too?
Add your prices in the cost section of the form. We never guess prices — a made-up figure is worse than none.
How to measure a room for paint
- Measure each wall from skirting to ceiling, then measure its width. Measure sloping walls separately rather than estimating them.
- Count doors and windows, then measure unusually large openings. The calculator uses practical defaults for ordinary openings.
- Measure the floor length and width too if you are painting the ceiling.
Metric: Enter wall dimensions in metres and openings in square metres.
Imperial: Enter dimensions in feet; the calculator converts the area and paint coverage for you.
How to work out how much paint you need
- Measure the length and width of the room, and the height from floor to ceiling.
- Add the two lengths and two widths together to get the perimeter, then multiply by the height. That is your wall area.
- Subtract the doors and windows — about 1.8 m² for a door and 1.4 m² for a window.
- Multiply by the number of coats you plan to apply. Two is normal.
- Divide by the coverage printed on the tin, usually around 10 m² per litre.
- Add about 10% for waste, then round up to the tin sizes your shop sells.
Assumptions
These are the defaults behind a new calculation. You can change the relevant values in the calculator; the result always shows the assumptions it used.
Paint coverage: 10 m² per litre
From the product label — Use the coverage printed on your chosen tin; surfaces and paint types vary.
Waste allowance: 10%
Industry rule of thumb — Covers roller loss, cutting-in and a small reserve for touch-ups.
The paint formula
Perimeter = (length + width) × 2
Wall area = perimeter × wall height
Area to paint = wall area (+ ceiling) − doors − windows
Total area = area to paint × number of coats
Litres = total area ÷ coverage × (1 + waste %)
Example: a 4 × 3 m room with 2.4 m ceilings
The perimeter is 14 m, so the wall area is 33.6 m². Take off one door (1.8 m²) and two windows (2.8 m²) and you have 29 m² to paint. Two coats makes 58 m². At 10 m² per litre that is 5.8 litres, and with 10% waste 6.38 litres — so you buy one 5 litre tin and one 2.5 litre tin, 7.5 litres in all.
Frequently asked questions
How much paint do I need for a 10 × 10 room?
For a 10 × 10 m room with 2.4 m ceilings, one door and two windows, you need roughly 21 litres for two coats with a 10% waste allowance — one 20 litre tub and one 2.5 litre tin. If you mean 10 × 10 feet (about 3 × 3 m), it is closer to 4 litres.
How many coats of paint should I use?
Two coats suit most jobs. Use three when you are covering a dark colour with a light one, or painting bare plaster or new plasterboard. One coat is only enough when you are refreshing the same colour.
How much paint do I need for 100 square metres?
At 10 m² per litre, 100 m² takes 10 litres per coat. For two coats with 10% waste that is 22 litres, so one 20 litre tub plus a 2.5 litre tin.
Should I include the ceiling?
Only if you are painting it. Turn on the ceiling switch above and we add the floor area to the area being painted. Ceilings often need a different paint, so many people calculate them separately.
Do I need primer as well?
Primer helps on bare plaster, new plasterboard, patched walls and when covering a strong colour. We do not add it automatically because it depends on your surface — run the calculator again with your primer coverage to size it.