CalcLibrary

Paint Calculator

Estimate how much paint you need for a room. Enter room dimensions, number of doors and windows, and coats to get the wall area, litres needed, and number of cans to buy.

Units
ft
ft
ft
Examples

A 4 m × 3.5 m bedroom with 2.5 m ceilings, 1 door, and 2 windows, 2 coats.

Paintable Wall Area
353.16 ft²
Paint Needed
1.73 gal
1 L Cans (Rounded Up)
7

You need 7 cans. Buy one extra for touch-ups.

Estimate based on smooth walls and 10 m²/L coverage. The cans count assumes 1 L cans — adjust for the can size you actually buy. Allow 5–10% extra for touch-ups.

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Examples

How It Works

Formula

Aw=2(L+W) H−1.89 D−1.4 WnA_w = 2(L + W)\,H - 1.89\,D - 1.4\,W_n

P=Aw⋅C10P = \frac{A_w \cdot C}{10}

Variables

LL

Room length(m)

WW

Room width(m)

HH

Room height(m)

DD

Number of doors (each assumed 1.89 m²)

WnW_n

Number of windows (each assumed 1.4 m²)

CC

Number of coats

AwA_w

Paintable wall area(m²)

PP

Paint required (10 m²/L coverage)(L)

Enter the room length, width, and height. The calculator computes total wall area, subtracts standard door and window areas, multiplies by the number of coats, and divides by paint coverage (10 m²/L) to estimate litres needed.

Frequently Asked Questions

01How much wall area does one litre of paint cover?
On average, one litre of interior wall paint covers about 10 m² per coat on smooth surfaces. Textured or porous surfaces may need 20–30% more paint.
02How many coats of paint do I need?
Two coats are standard for most interior walls. One coat may suffice if you are repainting the same colour. A primer coat is recommended when changing from dark to light colours.
03Should I paint the ceiling too?
This calculator covers wall area only. Ceiling area equals room length × width. Add that separately if needed. Ceiling paint is often a different formula.
04What door and window sizes does this calculator use?
Standard door: 1.89 m² (roughly 0.9 m × 2.1 m). Standard window: 1.4 m² (roughly 1.2 m × 1.2 m). If yours differ significantly, adjust the count accordingly.
05Should I buy extra paint for touch-ups?
Yes, it is wise to buy 5–10% extra for touch-ups and waste. The calculator rounds up to whole cans, which usually provides a small buffer.

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