How this mulch calculator works
The maths is simple: length × width × depth = volume in cubic metres. For a rectangular bed that's 4 m long by 2 m wide, mulched to 75 mm (0.075 m) depth, you need 4 × 2 × 0.075 = 0.6 cubic metres.
For circular beds, the formula is π × radius² × depth. The calculator handles that automatically — just enter the diameter.
We add a 10% waste margin to the recommended order quantity. That covers the reality of Australian mulch delivery: bulk loads settle during transport, some mulch compacts when you walk on it, and you'll always over-apply slightly near the edges of the bed. It's better to have half a bag left over than to run out on a Saturday afternoon.
How deep should mulch be?
For most established Australian garden beds, 75 mm is the sweet spot: deep enough to suppress weeds and hold moisture, shallow enough to breathe. Go deeper (100 mm) if you're fighting heavy weed pressure or planting in full sun in QLD, WA or NT. Go shallower (50 mm) for delicate groundcovers or young plantings.
Keep mulch 50–100 mm away from plant stems and tree trunks. Piled up against stems, it holds moisture against the plant and invites rot.
Choosing a mulch type
- Woodchip — all-purpose, chunky, long-lasting. Best for pathways and large garden beds.
- Bark mulch — finer than woodchip, tidier appearance. Favoured for formal gardens.
- Pine bark — lightweight, naturally acidic. Ideal for azaleas, camellias, and most Australian natives.
- Eucalyptus / hardwood chip — dense, great weed suppression, native-garden friendly.
- Cypress / red chip — naturally termite-resistant. The pick near buildings.
- Sugar cane — light, breaks down fast, adds nutrients. Best for vegetable gardens.
- Tea tree — dark, fragrant, native-look. Slow-breakdown decorative mulch.
- Pea straw / lucerne — nitrogen-rich, breaks down fast. Best for veggie patches and productive gardens.
Bag vs bulk: which is cheaper?
For anything over about 0.5 m³, bulk delivery is significantly cheaper than buying bags — often half the per-cubic-metre cost. But bulk usually has a minimum delivery fee ($40–80) and needs a spot a truck can reach. For small garden beds (under 0.3 m³) or jobs where a truck can't access, bags from Bunnings or your local hardware store make sense.
A 6×4 trailer holds about 0.7–1 m³ when loaded level. A tandem 8×5 holds 1.5–2 m³. Most landscape yards will load a trailer for you at no extra cost.