By Sam Alex, civil engineer · About the author
Landscape supplies are sold in cubic metres and tonnes, but projects are measured in square metres and millimetres. Getting from one to the other is where most over- and under-ordering happens. Here's a complete worked example for a typical backyard makeover.
The plan
- A new lawn area: 8 m × 5 m
- Garden beds along two fences: 12 m² in total
- A gravel path: 10 m long × 0.9 m wide
- A paved patio: 4 m × 3 m
1. Topsoil for the lawn
New turf wants 75–150 mm of good soil. I'll use 100 mm. 1. Area: 8 × 5 = 40 m² 2. Volume: 40 × 0.1 = 4.0 m³ 3. Allow 15% for settling: 4.0 × 1.15 = 4.6 m³ 4. At about 1,300 kg/m³: roughly 6 tonnes
Order 4.6–5 m³ of a screened sandy loam. Loosen the existing ground before spreading, so water can drain. The topsoil quantity calculator gives the weight with waste included.
2. Mulch for the garden beds
Mulch is usually spread 50–75 mm deep. More suppresses weeds better, but it shouldn't be piled against stems. 1. Area: 12 m² at 75 mm = 12 × 0.075 = 0.9 m³ 2. Plus 10% for settling: about 1 m³
3. The gravel path
A good gravel path has two layers: a compacted base and a decorative topping. - Base: 10 × 0.9 × 0.075 m = 0.675 m³ of road base. Allow 15% extra for compaction, giving about 0.78 m³, or roughly 1.5 tonnes at about 1,900 kg/m³. - Topping: 10 × 0.9 × 0.05 m = 0.45 m³ of 10–14 mm gravel. At about 1,600 kg/m³, that's 720 kg, so order about 0.8 tonnes. - Edging: 2 × 10 m = 20 m of steel or timber edging to hold everything in place.
The gravel calculator converts volume to tonnes for any layer.
4. The paved patio
- Area: 4 × 3 = 12 m²
- Pavers 230 × 115 mm (0.02645 m² each), 5% waste: 12 ÷ 0.02645 × 1.05 = 476.4, so 477 pavers
- Base: 100 mm of compacted road base = 1.2 m³, plus 15% ≈ 1.4 m³ (about 2.6 tonnes)
- Bedding sand: 30 mm = 12 × 0.03 = 0.36 m³, or about 580 kg of washed sand
- Jointing sand: usually a few bags, swept in after laying
- Edge restraint: 14 m of perimeter needs a concrete haunch or edging
See the paver calculator and sand calculator for the individual steps.
Putting the order together
| Material | Quantity |
|---|---|
| Screened topsoil | about 4.6–5 m³ |
| Garden mulch | about 1 m³ |
| Road base (path + patio) | about 2.2 m³ (about 4 t) |
| Decorative gravel | about 0.8 t |
| Washed bedding sand | about 0.6 t |
| Pavers | 477 |
| Edging | about 20 m (path) + 14 m (patio) |
Tips from the site
- Order bulk materials in one delivery where possible. Delivery fees add up quickly.
- Plan where each load will be tipped. Keep it close to where it's needed, on a tarp to protect the lawn and driveway.
- Hire a plate compactor for the base layers. A hand tamper can't get road base properly compacted.
- Set out falls: patios should fall away from the house, typically at least 1:100, so water doesn't pool against walls.
- Call before you dig (Before You Dig Australia) to locate underground services before any excavation.
Frequently asked questions
How much does a cubic metre of soil cover?
At 100 mm deep, 10 m². At 50 mm, 20 m².
Should I buy landscape materials by the tonne or the cubic metre?
Use whatever your supplier quotes, but convert with their density figure so you compare prices fairly.
How deep should a gravel path base be?
Typically 75–100 mm of compacted road base, with a 40–50 mm decorative topping.