Mulch Calculator Australia — Bags & Cubic Metres
Garden bed details
Measure length × width for rectangular beds. For irregular shapes, estimate in sections and add them together.
75 mm is the most common depth for Australian garden beds. Go deeper in hot, dry climates or where weed pressure is high.
Mulch type affects bag yield. Sugar cane and pea straw compress more than wood chip.
Mulch estimate
Quantities
Volume is calculated as area (m²) × depth (m). A 15% settling allowance is added on top, as all organic mulches compress under rain and foot traffic over the first few weeks. This calculator uses a 50 L bag as the standard unit — common for wood chip, bark, sugar cane and pea straw at Bunnings, Mitre 10, and landscape suppliers. For orders over 1 m³, buying in bulk from a landscape yard is typically 30–50% cheaper per cubic metre than bagged product.
Frequently Asked Questions
How deep should mulch be in an Australian garden?
The standard recommendation for Australian gardens is 75–100 mm. At 75 mm, mulch retains moisture, moderates soil temperature, and suppresses most annual weeds. Go to 100 mm in hot, dry climates (Perth, Adelaide, regional areas) or where weed pressure is severe. Keep mulch 50–75 mm away from plant stems and tree trunks to prevent collar rot. In fire-prone areas, some councils require non-combustible or low-combustibility mulch — check your local CFA/RFS guidelines before applying.
What is the difference between buying mulch in bags vs. bulk?
Bagged mulch (typically 30 L, 40 L or 50 L bags) is convenient for small jobs, easy to transport in a passenger car, and available at any hardware store. Bulk mulch ordered by the cubic metre from a landscape supply yard is significantly cheaper per unit volume — usually $40–$80/m³ delivered, compared to $120–$200/m³ equivalent in bags. The crossover point where bulk becomes economical is roughly 1–2 m³ (20–40 bags). Bulk orders require access for a truck, a tipping trailer, or a crane-placed bulka bag.
Which mulch type is best for Australian gardens?
Wood chip and bark mulch are the most durable (lasting 2–3 years before needing a top-up) and the best for moisture retention and weed suppression. Sugar cane mulch breaks down faster (6–12 months) but adds organic matter to the soil and is excellent around vegetables. Lucerne (alfalfa) and pea straw decompose quickly and add nitrogen — great as a soil conditioner around garden beds but require annual reapplication. In bushfire-prone areas, avoid fine-particle organic mulches close to buildings and use gravels or coarse bark instead.
How many 50 L bags of mulch in a cubic metre?
Exactly 20 bags at 50 L per bag equal 1 cubic metre. However, bagged mulch is often compressed — especially sugar cane and pea straw — so you may get slightly more coverage than the volume suggests once spread. Wood chip bags typically yield close to their stated volume. Always add 10–15% extra to account for settling.
Does mulch need to be replaced every year?
It depends on the type. Sugar cane and lucerne mulch decompose within 6–12 months and need annual replenishment. Wood chip mulch lasts 2–3 years. Coarse bark chip can last 3–5 years. Rather than a full replacement, most gardeners do an annual top-up of 25–50 mm to restore depth as the previous layer breaks down. Decomposed mulch is not wasted — it becomes organic matter in the soil, improving structure and fertility.