Landscaping
Mulch Calculator
Enter your garden bed dimensions in metres and the mulch depth in centimetres to get the volume in cubic metres and litres, plus a bag count if you're buying bagged mulch.
Formula tested · Local units · No sign-up
Project inputs
Enter measurements
Use your preferred units. Results update automatically.
Show the calculation methodFormula, conversions, rounding, and assumptions+
Volume = bed area × depth, converted to metres first — a 10 cm layer on a 20 m² bed is 20 × 0.1 = 2 m³ (2,000 litres).
Australian garden mulch is most often sold in bulk by the cubic metre from landscape yards, with bagged mulch (commonly 50–60 L bags — check your product) for smaller jobs. Bag counts round up to whole bags.
Real-world example
Worked example: 10 m × 2 m garden bed, 10 cm deep
- Area: 10 × 2 = 20 m².
- Convert depth: 10 cm = 0.1 m.
- Volume: 20 × 0.1 = 2.0 m³.
- Add 5% wastage: 2.0 × 1.05 = 2.1 m³ = 2,100 litres.
- If buying bags: 2,100 ÷ 50 = 42 bags of 50 L exactly — at this size, bulk m³ delivery usually makes more sense.
Order 2.1 m³ in bulk (or 42 bags of 50 L). Enter your supplier's price — advertised consumer prices in Australia normally include 10% GST.
Before you start
How to measure
- Measure beds in metres; for irregular native-garden beds, break the shape into rectangles, add the areas, and use the total-area mode.
- A 7–10 cm layer is a common target for water retention and weed suppression in Australian conditions; thinner layers suit annual top-ups.
- Keep mulch clear of plant stems and trunks, and don't bury drip lines deeper than they can wet the soil.
Local guidance
Notes for Australia
- Garden mulch in Australia is typically quoted per cubic metre from landscape suppliers, who often deliver by the trailer-load — the calculator's m³ total is the number to give them.
- Coarse mulches last longer and let rain through better than fine ones — coverage per m³ is the same, but the right depth differs by product; ask your supplier.
- GST is 10% and consumer prices are usually advertised GST-inclusive; trade or bulk quotes may be ex-GST.
Quick reference
Mulch depth quick reference (typical planning values)
| Application | Common depth |
|---|---|
| Annual top-up of beds | 3–5 cm |
| General garden beds | 5–7 cm |
| Water retention / weed suppression | 7–10 cm |
| Around trees and natives (clear of trunks) | 7–10 cm |
Planning values only — very fine mulch laid deep can repel water rather than hold it.
Good to know
Common mistakes to avoid
- Entering depth in millimetres into a centimetre field — 100 instead of 10 asks for ten times the mulch.
- Buying dozens of bags when a bulk trailer load would cover the same area — compare using litres (1 m³ = 1,000 L = 20 bags of 50 L).
- Skipping wastage: mulch settles quickly in hot weather, so 5% extra is a sensible buffer.
- Comparing GST-inclusive retail bags against an ex-GST bulk quote as if they were the same basis.
Need help?
Frequently asked questions
How many cubic metres for 25 m² of garden bed at 10 cm?
25 × 0.1 = 2.5 m³. With 5% wastage that's 2.625 m³ — most people would order 2.6–2.7 m³ in bulk.
How many 50 L bags for a 6 m² bed at 75 mm?
6 × 0.075 = 0.45 m³. With 5% wastage that's 0.4725 m³ = 472.5 litres, which is 10 bags of 50 L (472.5 ÷ 50 = 9.45, rounded up).
When does bulk delivery beat bags?
Roughly when the bag count gets awkward to transport — 1 m³ is already 20 bags of 50 L. Get your landscape yard's per-m³ price including delivery and compare it with the bag total this calculator shows.
Keep planning
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About this calculator
- Written by:
- BuildMeasure Editorial Team
- Technically reviewed by:
- Pending independent technical reviewer (formula unit-tested; see methodology)
- Last reviewed:
- 2026-07-16
- Formula version:
- 1.0.0
- Region reviewed for:
- Australia
- Spotted an error?
- Report a correction
Methodology
- Volume is computed as bed area × depth. You can enter the area directly or as length × width; either way all inputs are converted to SI units (metres) before any arithmetic to avoid unit drift.
- The wastage allowance is applied to the exact volume to cover settling and uneven spreading.
- Bag counts divide the total volume by the bag size you enter and round UP to whole bags, because you can't buy a fraction of a bag. The default bag size is a clearly-labelled common retail size (2 cubic feet in the US, 50 litres elsewhere) and is fully editable.
- The cost estimate simply multiplies the bag count by the price you enter. No prices are built in.
- The formula is covered by automated unit tests, including hand-calculated worked examples, and is versioned (see formula version on this page).
Sources & standards
- Unit definitions: Metric units throughout; 1 m³ = 1,000 litres.
- Bag sizes: 50 L is used as an editable default; Australian bagged mulch commonly ranges 25–70 L — check your product.
This tool provides a material estimate for planning purposes only. It is not a quotation. Bag sizes and coverage vary by product, and mulch settles over time — confirm quantities and product sizes with your supplier before buying.