How the calculation works
Walls = 2 × (length + width) × height − openings. Ceiling = length × width. Litres = area × coats ÷ coverage × (1 + allowance ÷ 100).
A measurement example
A 4 × 3 m room, 2.8 m high, with 3 m² of openings has 36.2 m² of walls. For illustration only, 2 coats at 10 m²/L with a 10% allowance require 7.964 litres, rounded up to 8.0 L. This is not a coverage promise for a particular paint.
What to allow for
This tool estimates a rectangular room. Measure recesses, beams and complex surfaces separately. Primer, filler and labour prices are excluded. Actual use depends on the surface, application method and product.