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Paint calculator — litres or gallons for a room

Enter room dimensions in metres and the coverage stated on your paint tin (m² per litre). Coverage varies by product and surface, so always use the manufacturer's figure.

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ツールとラベルは日本語です。以下の参考情報は英語のままです。

paint calculator

Paint needed
6.3L
In US gallons
1.66gal
Paintable area (one coat)
31.5m²

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Formula

litres = ([2(L + W)H − openings + ceiling] × coats) ÷ coverage (m²/L) · 1 US gal = 3.78541 L

Porous, textured or dark-to-light surfaces can need more paint or a primer. Round up to the tin sizes sold.

Worked examples

InputResult
4 × 3 m room, 2.5 m high, 3.5 m² openings, 2 coats, 10 m²/L31.5 m² × 2 ÷ 10 = 6.3 L (1.66 gal)
Same room with ceiling43.5 m² × 2 ÷ 10 = 8.7 L

Questions

How much paint do I need for a room?

Measure the wall area, subtract doors and windows, multiply by the number of coats and divide by the coverage on the tin. A 4 × 3 m room with 2.5 m walls needs about 6.3 L for two coats at 10 m²/L.

How many square feet does a gallon cover?

Many labels state roughly 350–400 ft² per US gallon for one coat, but use your product's figure. 1 m²/L ≈ 40.7 ft²/gal.

Should I subtract windows?

Yes for large openings. Leaving them in gives a more conservative estimate.

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