Mulch Calculator
Enter the length and width of your bed, the depth you want in centimetres, and your bag size in litres. The calculator converts everything to cubic metres, rounds up to whole bags, and totals the cost if you enter a price per bag.
Garden-centre mulch calculators usually push one brand and one bag size. This one is brand-neutral, metric, and honest about the point where a delivered bulk skip of a cubic metre or two beats carrying dozens of plastic bags home.
How to use
- Measure the bed's length and width in metres — for an odd shape, break it into rectangles and add the areas as a length × width pair.
- Pick your depth: 5 cm is the standard weed-suppressing layer, 7–8 cm for bare soil or topping up old mulch.
- Enter the bag size printed on the bag (commonly 50–100 L) and the price if you want a total; the result rounds up to whole bags.
Frequently asked questions
How deep should mulch be?
5 cm blocks most weeds and holds moisture well. 7–8 cm suits bare, dry soil or a refresh over old mulch. Beyond 10 cm you risk starving roots of air, and never pile mulch against trunks or stems — leave a hand-width clear to avoid rot.
How many 50-litre bags make a cubic metre?
Twenty. That is the bulk-vs-bags crossover in practice: once you need roughly a cubic metre or more, delivered bulk mulch is usually cheaper per m³, saves dozens of bags, and can be barrowed straight onto the beds.
Do I need to remove old mulch first?
No — loosen it with a fork and top up to the target depth. Only remove it if it has matted into a water-shedding crust or shows fungal growth; otherwise the old layer composts in place and feeds the soil.
Does mulch attract pests?
Properly aerated mulch at the right depth attracts worms, not trouble. Problems come from too-deep layers and mulch piled against stems, which create the damp hiding spots slugs and rodents like.