Paint Calculator: How Many Litres of Paint for Your Room?

Enter the room length, width and height, choose whether to paint the ceiling and enter the doors and windows. The calculator gives the paintable area, the litres of paint and the number of 4-litre cans.

FreeNo sign-upRuns in your browserUpdated 2 Nov 2026
Check the tin. About 10 m² per litre is common, which is roughly 107 sq ft.
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Estimates only. Check important results before you rely on them.

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How to use this calculator

  1. Enter the room length, width and height.
  2. Choose whether the ceiling is painted.
  3. Enter the number of doors and windows and the coats.
  4. Enter the coverage printed on your paint tin and read the litres.

The formula

Wall area = 2 × (Length + Width) × Height. Ceiling area = Length × Width. Paintable area = Walls + Ceiling − Openings. Litres = Paintable area × Coats ÷ Coverage × (1 + Wastage%). A door is taken as 1.8 m² and a window as 1.4 m².

Worked example

A 14 ft × 12 ft room, 10 ft high with the ceiling, 2 doors and 3 windows: walls 48.3 m² + ceiling 15.6 m² − 7.8 m² openings = 56.1 m² (604 sq ft). Two coats at 10 m² per litre with 5% wastage need 11.8 litres, which is three 4-litre cans, plus 5.9 litres of primer.

Understanding your result

Rough or porous walls absorb more paint, so coverage may be lower than the tin says. Dark colours over light, or the reverse, often need an extra coat.

When to use it

  • Buy the right amount of paint and avoid a second trip.
  • Compare the cost of one room and several rooms.
  • Plan a repaint.

Assumptions and limits

These are planning estimates. Real use depends on material quality, site conditions and workmanship. Confirm quantities with your engineer or contractor before ordering. Door and window sizes are standard assumptions. Trims, skirting and textured finishes are not included.

Frequently asked questions

How much paint do I need for a 12 × 14 ft room?

About 11 to 12 litres for two coats on walls and ceiling with typical openings.

How much area does 1 litre of paint cover?

Usually 9 to 12 m² (100 to 130 sq ft) per coat. Check the tin.

How many coats do I need?

Two coats is standard. A lighter colour over a dark wall may need three.

Do I need primer?

On new or very porous plaster, yes. The tool shows the primer for one coat.

Do I subtract doors and windows?

Yes. Enter their number and the tool deducts a standard size for each.