Free tool
Soil and mulch calculator
Area and depth in, cubic metres, bags and trailer loads out.
Landscape supplies are sold by the cubic metre in bulk and by the bag at a hardware store, and the two are hard to compare in your head. One cubic metre is forty 25 litre bags, which is usually the moment people decide to order bulk.
The sum
Area times depth. A 5m by 3m bed at 75mm is 5 x 3 x 0.075, which is 1.125 cubic metres. As with concrete, the trap is the depth: 75mm is 0.075m.
Depths that work
| Job | Depth |
|---|---|
| Mulch on an established garden bed | 50 to 75mm |
| Mulch on a new bed, for weed suppression | 75 to 100mm |
| Topsoil for a new garden bed | 200 to 300mm |
| Underlay before laying turf | 100mm |
| Topdressing an existing lawn | 10 to 20mm |
Mulch deeper than about 100mm starts working against you. It keeps water off the root zone rather than in it, and piled against a trunk it holds moisture where the plant least wants it. Keep it clear of stems.
Bags, bulk or a trailer
Forty 25 litre bags to the cubic metre, twenty 50 litre bags. Past about half a cubic metre, bulk is cheaper per unit and much less carrying.
A standard 6x4 box trailer holds roughly 0.7 of a cubic metre loaded level with the sides. Heaped it will hold more, but soil is heavy: a cubic metre of damp garden mix runs well over a tonne, which is past what most box trailers and plenty of tow vehicles are rated for. Two trips is cheaper than a spring.
It settles
Mulch drops noticeably in the first few months and garden mix compacts as it wets in. Order for the depth you want after it has settled rather than the depth on the day, or plan to top up in autumn.
Delivery on the border
Landscape yards on the Albury Wodonga corridor deliver both sides of the river and most have a minimum load, usually a cubic metre or two, with a flat delivery fee that makes small orders poor value. If you are under a cubic metre, bags or a trailer usually win.
Common questions
How much mulch do I need?
Multiply the bed area in square metres by the depth in metres. A 5m by 3m bed at 75mm needs 1.125 cubic metres. For an established bed, 50 to 75mm is the usual depth; for a new bed being mulched for weed suppression, 75 to 100mm.
How many bags of mulch are in a cubic metre?
Forty 25 litre bags, or twenty 50 litre bags. Past about half a cubic metre, buying bulk is cheaper and a great deal less carrying.
How much soil fits in a 6x4 trailer?
Roughly 0.7 of a cubic metre loaded level with the sides. Be careful heaping it: a cubic metre of damp garden mix weighs well over a tonne, which is beyond the rating of most box trailers and many tow vehicles.
How deep should mulch be?
50 to 75mm on an established bed, up to 100mm on a new one where you want weed suppression. Deeper than that starts shedding water away from the root zone rather than holding it, and it should always be kept clear of trunks and stems.
How much topsoil do I need before laying turf?
About 100mm of underlay over a prepared base. For a new garden bed rather than lawn, 200 to 300mm of topsoil is the usual range depending on what is going in it.