Mulch is light, cheap and easy to over-order — and easy to over-apply, which is worse. The right depth suppresses weeds and holds moisture. Too deep starves roots of air and rots the base of whatever you spread it around.
Beds, borders and around trees. Enter the area and the depth, and get bags or a bulk load.
Works in metric and US imperial — you choose at the start and can switch at any time. Every figure this calculator uses is published with its source, and the result comes with a printable order sheet. No account, no email, and nothing you type leaves your browser.
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Area × depth, plus a settlement allowance, converted to bags or a bulk load. Density is the catch: bark chip runs around 400 kg/m³ and wood chip 350 kg/m³ dry, but wet bark can weigh half as much again — which is a good reason to order by volume where you can. The calculator counts bags for the size you pick, because "a bag of mulch" spans a wide range.
A 8 × 2 m bed — 16 m² — mulched at the standard 75 mm is 1.2 m³ of bark before settlement. That is a solid trailer-load, or around twenty typical bags. Composted soil conditioner goes on thinner, at about 50 mm, so the same bed needs a third less.
Mulch onto damp soil, not dry. Mulch slows evaporation, which means it also slows soil getting wet — spread it over bone-dry ground in summer and you lock the dryness in. Water first, or wait for rain. And if you are using fresh wood chip, keep it on the surface: dug in, it locks up nitrogen as it breaks down.
50–75 mm (2–3 in) is the working depth, and 100 mm (4 in) is the maximum. Depth suppresses weeds up to a point, then stops helping and starts harming — waterlogging, poor air exchange, and roots growing up into the mulch. If a bed still weeds through at 75 mm, the problem is usually perennial roots left in the soil, not insufficient mulch.
No — keep it 75–100 mm clear of trunks and stems, always. Mulch against bark rots it. This is the most common and most damaging mulching error, and it is entirely avoidable.
It suppresses seedlings; it does not kill established perennial weeds. Bindweed and couch grass will come straight through 100 mm of bark, and you will then be weeding through mulch, which is far worse than weeding through soil. Weed first, and weed properly.
Bark and wood chip break down and want topping up every year or two. That is a feature, not a flaw — the breakdown is the material improving the soil — but budget for it rather than being surprised.