Mulch calculator

Work out how much bark or wood-chip mulch you need for a bed or border, or — if you already have a set number of bags — how far they'll stretch.

LengthWidthDepthWaste allowance (%)

Result

Mulch required

Bags needed (50L)

How to use this calculator

Measure the area you're mulching.
Set the depth — 5–7cm is typical for weed suppression and moisture retention.
Read the volume required and the equivalent number of bags, or use reverse mode if you already have bags on hand.

Bag count assumes a standard 50L bag — loose-tipped bulk loads are cheaper for larger areas.
Mulch breaks down and compacts over a season, so a yearly top-up is normal.

Technical details: what the fields mean

Length length: The longest side of the area to mulch.
Width width: The other side of the area to mulch.
Depth depth: Mulch layer thickness — 5–7cm suppresses weeds without smothering low plants.
Waste allowance wastePercent: Extra to cover an uneven surface and settling over the season.

Methodology

Volume = length × width × depth, increased by the waste allowance. Bags assume a standard 50L bag.

Worked example

5m × 2m border, 6cm mulch, 10% waste

Inputs: length=5, width=2, depth=6, wastePercent=10

Result: 0.66 m³ required, 14 bags

Practical guidance

Keep mulch a few centimetres clear of plant stems and tree trunks to avoid rot.
Wood-chip mulch is cheaper and better for paths; bark mulch looks tidier in ornamental beds.

Common mistakes

Piling mulch directly against stems and trunks ('mulch volcanoes'), which encourages rot and pests.
Under-ordering because settling over the season isn't accounted for.

5–7cm is typical — enough to suppress weeds and retain moisture without smothering low-growing plants.

Use reverse mode below: enter your bag count, width and depth to see the length you can cover.