Landscape materials are sold in a confusing mix of units: cubic metres for mulch, soil and gravel at landscape yards, tonnes at quarries, and handy bags in litres or kilograms at the hardware store. Everything starts from the same volume calculation, then converts to however the supplier sells it.
Volume first
volume = area × depth. Convert depth to metres before multiplying: 50 mm is 0.05 m. For beds with curved edges, measure the longest length and the average width, or split the bed into shapes.
Weight from volume
| Material | Approx. density |
|---|---|
| Crushed stone / gravel | 1.5–1.7 t/m³ |
| Pea gravel | about 1.55 t/m³ |
| Sand (dry) | 1.5–1.6 t/m³ |
| Topsoil | 1.2–1.4 t/m³ |
| Road base (compacted) | 2.0–2.2 t/m³ |
| Mulch | about 0.35–0.45 t/m³ |
Wet material is heavier, often by 10–20%, which matters when you're buying by weight or checking a trailer's payload.
Recommended depths
| Use | Depth |
|---|---|
| Mulch or bark in beds | 75–100 mm |
| Decorative gravel on paths | 40–50 mm over a compacted base |
| Gravel driveway surface | 40–50 mm over 100–150 mm of road base |
| Topsoil for new lawn | 100–150 mm |
| Play sand | 300 mm or more |
What a cubic metre covers
One cubic metre covers 20 m² at 50 mm, about 13 m² at 75 mm and 10 m² at 100 mm.
Bags vs bulk
A cubic metre is 20 bags of 50 L mulch, 40 bags of 25 L, or about 80 bags of 20 kg gravel. Bulk from a landscape yard is usually cheaper above about half a cubic metre, as long as the truck can tip somewhere handy.
Think about delivery too. Bulk loads are tipped on a driveway or dropped in bulk bags, then barrowed to where they're needed. Bags can go straight to the back garden, but they're slower and leave a lot of plastic.
Compaction and settling
Base materials compact by 15–25%, and loose soil settles 15–20%. Add these allowances to the volume, or you'll come up short. Mulch breaks down over a season and needs topping up, typically 25 mm a year.
Under the gravel
A weed membrane under decorative gravel saves hours of weeding. On paths and drives, edging keeps stone out of lawns and beds and is worth including in every quote.
Use the gravel, mulch, topsoil and sand calculators. Each shows volume, weight, bags and bulk quantities together.
A worked example
A 12 × 3 m gravel path at 50 mm: 36 m² × 0.05 m = 1.8 m³. At 1.6 tonnes per cubic metre that's 2.9 tonnes. Add 5%: order 1.9 m³, plus enough weed mat to cover 36 m² with overlaps.
Ordering tips
- Ask what the supplier's "load" or "bag" actually holds. Sizes vary.
- Check delivery access and where the load will be tipped. A tipper truck needs firm ground and clearance.
- Put down a tarp before a bulk load is tipped on a driveway. It saves an hour of clean-up.
- Order a little extra on decorative gravel. Matching it later from a different quarry batch can be hard.
Choosing the right material
- Paths and drives need angular, crushed stone that locks together. Round pea gravel rolls underfoot and migrates, so it's best for borders and drainage.
- Bases under paving and sheds need a well-graded material with fines (road base or crushed rock) that compacts hard.
- Drainage needs clean stone with no fines, so water can flow through it.
- Bedding sand for pavers is sharp, coarse sand, not soft building sand, which stays plastic and moves.
- Mulch varies from fine shredded bark, which breaks down fast and feeds the soil, to large nuggets that last longer but blow and float away.
When in doubt, ask the supplier what they recommend for the use. A cheaper material that doesn't suit the job costs more in callbacks.
Common questions
How much does a cubic metre of mulch weigh?
A cubic metre of mulch weighs roughly 350–450 kg dry, and more when wet, much lighter than stone. That's why trailers carry a lot more mulch than gravel.
Can my ute or trailer carry it?
Check the payload first. Many utes and single-axle box trailers can't legally carry a full cubic metre of gravel, which weighs around 1.6 tonnes. The material weight calculator works out how many trips a load needs.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check the NCC, Australian Standards and your building surveyor or certifier for your project.