Mulch calculator
Under two inches, light reaches the soil and weed seed germinates straight through. Over four inches, water struggles to get down to the roots and the mulch itself starts to shed rain sideways. Three inches is the figure every extension service settles on, and it is the depth this page defaults to.
One cubic yard of mulch covers about 100 square feet at 3 inches deep, which is the depth that suppresses weeds without starving roots of water. Multiply the bed area by the depth, then divide by bag volume — a standard 2 cubic foot bag is about 56 litres.
How to work out mulch
Mulch is the one garden material where buying loose is dramatically cheaper, and the crossover comes sooner than people expect. One cubic yard is about fourteen of the two-cubic-foot bags. At typical retail pricing, a bed needing more than eight or ten bags is usually cheaper delivered loose, even after the delivery charge — and it saves an afternoon of splitting plastic. The catch is that loose mulch arrives as a heap on the drive and has to be moved that day.
Questions
About 13.5 bags of 2 cubic feet, so buy 14. In metric, about 15 bags of 50 litres to the cubic metre.