How Much Paint Do I Need?

Paint calculator: enter the product's coverage

The calculator uses net area, coat count, coverage per litre and an optional allowance. Enter the coverage rate from the exact product's label or technical sheet. A lower coverage rate means you need more paint for the same area.

Calculate walls, ceilings, trim and preparation products separately where they use different coatings. The result is a material estimate, not a quote for labour or a promise of the final quantity needed.

Measure a room in square metres

For walls of a consistent height, add the lengths of all the walls and multiply by height. Subtract large openings that will not be painted. Measure each wall separately where ceiling heights vary, and divide irregular shapes into simpler rectangles or triangles.

A ceiling's area is usually its length multiplied by width for a flat rectangular room. Sloping ceilings, deep reveals, cupboards and decorative details need their own measurements. Use metres throughout rather than mixing metres and centimetres.

For measurements in feet, multiply a length by 0.3048 to convert to metres. Convert square feet to square metres by multiplying by 0.092903. The calculator can also accept square feet and convert the area for you.

Paint coverage calculator: a worked room example

Imagine a rectangular room 4 m long, 3 m wide and 2.4 m high. The wall perimeter is 14 m, giving 33.6 m² of wall area. Subtract 3.6 m² of unpainted openings to leave 30 m².

For two coats at an example coverage of 12 m² per litre per coat: 30 × 2 ÷ 12 = 5 litres. Add a 10% example allowance and the estimate becomes 5.5 litres. Round your purchase up to suitable pack sizes after checking the product and actual surface.

The ceiling in that room is 12 m² and needs a separate calculation if it uses a different paint. Primer or sealer is also separate. These are worked measurements and assumptions, not a specification for every room.

What changes the amount of paint?

Do not stretch a coating beyond its specified spreading rate to make a tin last. Too little material can compromise the intended finish.

How many coats should you allow?

Use the coating system's instructions for the substrate and colour. A topcoat's coat count does not include every primer or sealer beneath it. New linings, stains and difficult colour changes may need a different system from a sound maintenance repaint.

Read primer versus undercoat and wall preparation before finalising the materials list. Follow drying intervals as well as coat count.

For an initial estimate, the calculator lets you test different coat counts without hiding the assumptions. Confirm the actual specification before purchasing.

Use the estimate to prepare a better brief

Write down room dimensions, included surfaces, existing colours and the condition of the coating. Add photos of repairs, peeling and textured areas. These details help us assess preparation and quantities as part of a quote.

Use our interior painting guide to connect measurements with access, colour and timing. Keep leftover material labelled and stored as directed, and arrange an appropriate recovery or disposal route for anything you no longer need.

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