To determine how much paint to buy for your DIY job (if you're in a country that's adopted the metric system), find the square meterage of the area you plan to paint and divide by the number of square metres covered by a litre of paint.

  • Total wall area: Total length of all walls x wall height

  • Unpainted areas:

    • Window area = window height x window width x number of windows

    • Door area = door height x door width x number of doors

  • Paintable wall area: Total wall area – window area – door area

  • Paint to order:

    • Paintable area 1500 = number of litres needed for smooth walls

    • Paintable area 1350 = number of litres needed for rough, textured walls or unpainted wallboard