Compost & Mulch Calculator

Find the litres of compost, mulch or topsoil needed to cover a bed or border to a chosen depth, plus a rough number of bags and barrowloads.

How it works

Cover a square metre one centimetre deep and you use ten litres of material, so the litres needed are the area in square metres times the depth in centimetres times ten:

Litres = length m × width m × depth cm × 10

A weed-suppressing mulch is usually 5 to 8 cm deep; a light topdressing of compost is 1 to 2 cm. The tool estimates 50 litre bags and barrowloads (a full garden barrow holds roughly 90 litres). Keep mulch pulled back from plant stems.

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This tool is a planning aid and simply does the maths from the numbers you enter. Order a little extra to allow for settling. Page updated 18 Sep 2026.