How much paint do I need?

The transparent formula

Litres = area × coats ÷ coverage per litre. If 30 m² receives two coats and the chosen product states 10 m²/L for the relevant conditions, the estimate is 30 × 2 ÷ 10 = 6.0 L.

Reference table at an example 10 m²/L coverage

The 10 m²/L figure is an example for illustrating the arithmetic, not a universal paint specification. Use the coverage stated by the manufacturer of the product you intend to use.

Calculate room wall area

For a rectangular room, calculate each wall or use perimeter × height. A 4 m × 3 m room with 2.4 m walls has a perimeter of 14 m, giving 33.6 m² of gross wall area. Large doors and windows can then be deducted if appropriate.

Worked room example

Suppose gross wall area is 33.6 m² and openings total 4.0 m². Paintable area is 29.6 m². Two coats at an assumed 10 m²/L gives 5.92 L. The container sizes actually available will determine the purchase quantity.

Coverage is not constant across every job

Surface texture, porosity, application method and product specification can affect real consumption. The safest calculator input is the coverage information for the exact product and surface rather than a generic internet average.

Keep ceilings and trim separate

Different surfaces often use different products. Calculate walls, ceilings and woodwork separately so a single total does not conceal different coverage rates or coat counts.