Paint Quantity Calculator

How much paint do you need?

The quantity depends on three things: the area to paint, the number of coats and how many square metres one litre covers. The calculation is litres = area × coats / spreading rate. A waste allowance is added and the result is divided by the can size and rounded up.

Working out the area

In a rectangular room the wall area is 2 × (length + width) × height. If the ceiling is painted too, add length times width. Doors, windows and other openings are deducted. The calculator does this for you, or you can type the area directly.

What is the spreading rate?

It is the area one litre covers in a single coat, given in m²/L. You will find it on the can or in the product data sheet. Water based interior paints are roughly 8 to 14 m²/L per coat. Rough or porous surfaces, and going from a dark colour to a light one, reduce the rate. That is why the calculator does not impose a value and expects the figure from the data sheet.

Example

A room of 5 m × 4 m with 2.7 m high walls has 48.6 m² of wall and 20 m² of ceiling. Deducting 3.5 m² of doors and windows leaves 65.1 m². Two coats at 10 m²/L need 13.02 litres, or 14.3 litres with 10 percent waste. That is one 15 litre can.

Limits

If primer, filler and ceiling paint are different products, calculate each with its own rate. On exterior walls the surface texture changes consumption a lot, so use the rough surface figure from the data sheet.