How much topsoil do I need?
The volume is easy. What decides whether a soil job goes well is the two things the sum doesn't tell you: what you're actually buying, and how far it will drop once it's wet.
Soil settles — order for that
Loose soil off a truck is full of air. Water it in, walk on it, let a fortnight of rain go through it and it drops. On a fresh spread, 10 to 15% is the normal allowance. Order to the finished level and you'll be back at the yard for another half metre, which is a second delivery fee on a job you already quoted.
Where it matters most is anywhere the finished level is fixed by something else — soil that has to finish flush with a path, a garage slab or a set of steps. Order the settling in, screed it slightly proud, and let it come down to level on its own.
A worked example — a spread bed
Fifty square metres of new garden bed, 150mm of screened topsoil, 10% for settling:
- Finished volume: 50 × 0.15 = 7.5 m³
- Plus 10% settling: 7.5 × 1.1 = 8.25 m³
- Rounded to how it's sold: 8.5 m³
- Weight, at 1.3 t/m³: 8.25 × 1.3 = 10.73 tonnes
Ten and a half tonnes is a truck, not a trailer. Half a cubic metre of screened topsoil already weighs 650kg, which is over the payload of a typical unbraked box trailer before you've filled it level with the sides.
A worked example — a raised bed
A raised bed is a different sum in one way only: the depth is the box's own depth, and there's nothing to settle into.
- Bed 2.4m × 1.2m, 400mm deep: 2.88 m² × 0.4 = 1.15 m³ of garden mix
- Fill the bottom 150mm with something cheaper and only the top 250mm is mix: 2.88 × 0.25 = 0.72 m³
That part-fill is worth doing on any bed deeper than about 300mm sitting on open ground. Coarse organic material, old sticks, spent potting mix or plain screened fill in the bottom third, good mix on top. Roots reach into it, it breaks down over a season, and you've bought a third less premium mix. Don't do it if the bed sits on concrete or pavers — see drainage below.
What each soil is actually for
| Soil | Density | Use it for |
|---|---|---|
| Screened topsoil | 1.3 t/m³ | General bed-building and bulk filling. Screened through a 10mm mesh, so no rocks or roots |
| Garden / veggie mix | 1.0 t/m³ | Veggie beds and planting beds. Higher organic content, holds moisture, feeds |
| Sandy loam | 1.4 t/m³ | Under new turf and for levelling lawns. Drains, screeds flat, doesn't set like clay |
| Potting / raised-bed mix | 0.5 t/m³ | Pots, planters and shallow boxes. Light and free-draining, so it doesn't compact under its own weight |
One cubic metre covers 10 m² at 100mm, 6.7 m² at 150mm and 3.3 m² at 300mm.
The "topsoil" trap
Topsoil isn't a graded product with a set specification — it's whatever the yard is calling topsoil that week, and at the cheap end it's often subsoil, site fill or straight clay with a bit of colour through it. Spread that over a bed and nothing grows, and you find out three months later.
Before you order a big load, ask three questions: is it screened, and to what size? What's gone into it? Can I look at a sample? Then do the squeeze test — grab a wet handful. Good loam crumbles when you open your hand. Clay-heavy fill holds the shape of your fingers and stays sticky. If the yard won't let you look at it, buy somewhere else.
Drainage, or you've built a bathtub
A raised bed sitting on open soil drains through the bottom on its own — unless what's underneath is compacted clay, in which case break it up with a fork before you fill.
A bed on concrete, pavers or a balcony has nowhere to go. It needs drainage holes or gaps in the base, something coarse across the bottom, and a lighter mix that doesn't hold water. Fill a sealed box with heavy screened topsoil and you have a bathtub with plants in it, and the first thing that happens is the roots drown.
Quoting a soil job
Soil is heavy and it's almost never dropped where it's needed. Price the delivery, the spread and the barrow runs separately from the material. A five-metre load through a side gate is a completely different day to a five-metre load a bobcat can push straight in.
Worked out the soil. Now price the job.
Yamate turns your metres and hours into a quote the customer can accept on their phone, then an invoice, then a payment — with GST handled and the follow-ups chased for you.
Try Yamate free → Free to try · no card · sign in with a link, no password to rememberTopsoil & raised-bed soil FAQ
How much topsoil do I need for 50 square metres?
At 150mm deep that's 7.5 cubic metres finished, or about 8.25 once you allow 10% for settling — so order 8.5. In screened topsoil that's roughly 10.7 tonnes.
How deep should topsoil be?
10 to 20mm for top-dressing a lawn, 50 to 100mm as underlay under new turf, 150 to 300mm for a new garden bed, and 300 to 500mm for a raised veggie bed. Deeper isn't better on a spread — it just costs more and settles more.
Does topsoil settle after you spread it?
Yes. Loose soil off a truck is full of air and drops around 10 to 15% once it's watered in and walked on. Order the allowance in, especially where the finished level has to match a path or a slab.
How much does a cubic metre of topsoil weigh?
Screened topsoil is about 1.3 tonnes a cubic metre. Garden mix is around 1.0, sandy loam 1.4 and potting mix only 0.5. Wet soil weighs more than the figure on the price list.
How much soil for a 2.4m × 1.2m raised bed?
At 400mm deep, 1.15 cubic metres. Part-fill the bottom 150mm with cheaper material and you only need 0.72 of good mix — as long as the bed sits on open ground, not on concrete.
What's the difference between topsoil and garden mix?
Screened topsoil is soil, screened to take the rocks and roots out — good for bulk filling and building beds up. Garden mix has compost and organic matter blended through it and is what you want in the top layer where things are actually growing.
Can I put a raised bed on concrete?
You can, but it needs drainage holes or gaps in the base and a lighter free-draining mix. A sealed box full of heavy topsoil holds water at the bottom and drowns the roots.
Other calculators you'll want
General information for Australian trades, and an estimate only — not tax, financial or legal advice. It is not engineering, building or design advice either: a calculator works out a quantity from the figures you enter, and anything that needs sign-off still needs your engineer, certifier or building surveyor. Bulk densities are typical figures from Australian landscape suppliers and vary with moisture, blend and screening — confirm with your own supplier before ordering. Soil products are not sold to a single national specification, so inspect a sample before committing to a large load. This calculator is a materials estimate to help you order and quote, not a horticultural specification.