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Paint Calculator: How Many Litres for Your Room

Enter room length, width and height, the number of doors and windows, coats and the coverage on your paint tin. You get litres to buy and a pack combination.

Paint to buy

9L

Area to paint
40.23 m² · 433 sq ft
Exact need
8.05 L
Suggested packs
2 × 4 L + 1 × 1 L

Door taken as 2.1 × 0.9 m, window 1.2 × 1.2 m. Primer and putty are not included.

Show working
  1. 2 × (4 + 3.5) × 3 = 45 m²
  2. 45 − 1 × 1.89 − 2 × 1.44 = 40.23 m²
  3. 40.23 × 2 ÷ 10 = 8.05 L

How to use

  1. Enter room length, width and height.
  2. Enter doors and windows, and tick the ceiling if you paint it too.
  3. Set coats and coverage per litre (from the tin) to see litres and packs.

Good to know

Wall area = 2 × (length + width) × height, minus 1.89 m² per door (2.1 × 0.9 m) and 1.44 m² per window (1.2 × 1.2 m), plus the ceiling if ticked. Litres = area × coats ÷ coverage per litre per coat.

Coverage depends on the product and the surface. Interior emulsions often cover about 9–14 m² (100–150 sq ft) per litre per coat on smooth putty; textured or porous walls take more. The default 10 m²/L is a cautious middle; use the figure printed on your tin.

Primer and putty are separate jobs with their own coverage. Packs are suggested from common 20, 10, 4 and 1 litre sizes; buying one larger pack is often cheaper than several small ones.

Questions

How much paint for a 12×12 ft room?

With a 10 ft ceiling, walls are 480 sq ft; minus one door and two windows about 430 sq ft (39.8 m²). Two coats at 10 m²/L need about 8 litres.

How many coats do I need?

Two coats of finish paint is standard. A big colour change may need a third.

What coverage should I enter?

The spreading rate on your tin, per coat. If it says “for 2 coats”, halve the area before entering.

Does it include primer?

No. Primer is applied once and has its own coverage; calculate it separately with 1 coat.

Why is the answer rounded up?

Paint is sold in whole packs and running short mid-wall leaves patches, so litres are rounded up.

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