Gravel, Sand & Soil Calculator
Work out how many cubic metres, tonnes and bags of gravel, sand, topsoil, compost or mulch you need for a rectangle or a circle.
Weights use typical loose densities (gravel (20 mm stone) 1.6 t/m³, crusher run / road base 1.9 t/m³, building sand 1.6 t/m³, topsoil 1.4 t/m³, compost 0.6 t/m³, bark chips / mulch 0.35 t/m³). Moisture and grading can change them by about 15%, so confirm with your supplier.
Coverage by depth
How far one cubic metre goes.
| Depth | Area per m³ | m³ per 10 m² |
|---|---|---|
| 25 mm | 40 m² | 0.25 m³ |
| 50 mm | 20 m² | 0.5 m³ |
| 75 mm | 13.3 m² | 0.75 m³ |
| 100 mm | 10 m² | 1 m³ |
| 150 mm | 6.7 m² | 1.5 m³ |
| 200 mm | 5 m² | 2 m³ |
How the calculation works
Volume is the area multiplied by the depth: for a rectangle length × width × depth, and for a circle π × (diameter ÷ 2)² × depth. The calculator then adds your allowance for waste and settling, multiplies the volume by the material's density to get the weight in tonnes, and divides by your bag size to give a whole number of bags (rounded up).
Depth is the part people get wrong, because a depth in millimetres has to be divided by 1000 to use it with lengths in metres. The calculator does that for you.
Three worked examples
A path 10 m long and 1 m wide, covered with 50 mm of gravel. The volume is 10 × 1 × 0.05 = 0.5 m³. Add 10% for settling and spillage and you need 0.55 m³. At about 1.6 tonnes per cubic metre, that's 0.88 tonnes, or 22 bags of 40 kg.
A driveway 12 m long and 3 m wide, with a 100 mm base of crusher run. The volume is 12 × 3 × 0.1 = 3.6 m³. Crusher run is compacted with a plate compactor, so allow about 15% extra: 4.14 m³. At about 1.9 tonnes per cubic metre that comes to 7.9 tonnes.
A circle 3 m across, covered with 75 mm of gravel. The area is π × 1.5² = 7.07 m², so the volume is 7.07 × 0.075 = 0.53 m³. With 10% extra that's 0.58 m³, or about 0.93 tonnes.
To check any of these, switch the shape to Circle or change the depth in the calculator above.
How deep should it be?
Depth is the number that changes the answer most, and the one people guess. These are typical depths, but your supplier or the product's instructions come first.
| Job | Typical depth | Material |
|---|---|---|
| Decorative gravel on a base or membrane | 25–50 mm | Gravel |
| Gravel path with no base | 50–75 mm | Gravel |
| Driveway or load-bearing base | 100–150 mm, compacted | Crusher run |
| Bedding layer under paving | 25–50 mm | Building sand |
| New lawn | 100–150 mm | Topsoil |
| Flower or veg bed | 100–150 mm (more for raised beds) | Topsoil, compost |
| Mulch around plants | 50–75 mm | Bark chips |
Volume or weight: what will the supplier quote?
Suppliers sell by the cubic metre, by the tonne, or in bulk bags, and they don't always use the same one. That's why the calculator gives you all three. If a supplier quotes in tonnes, use the Weight tile. If they quote in cubic metres, use Volume. If you're buying bags, use Bags.
One thing worth knowing if you're collecting the load yourself: gravel is heavy. A cubic metre weighs about 1.6 tonnes, and many bakkies and pick-ups have a payload of only around a tonne (check the figure for yours). So a legal load of gravel in a bakkie is often well under a cubic metre. It's one of the reasons a delivery truck is often cheaper than a few trips.
Mistakes that cost you a second delivery
- Mixing up millimetres and metres. 50 mm is 0.05 m. Typing 50 into a calculator that expects metres gives you a pile the size of a house. This calculator takes depth in mm for you.
- Forgetting the extra. Loose material settles and compacts, and some is lost when you spread it. Add 5 to 10%, and up to 15–20% for a compacted base.
- Forgetting the base layer. A path or driveway often needs a base under the top layer. Work out each layer separately.
- Ignoring wet material. Rain makes sand and soil heavier, by up to about a quarter in the case of sand. If you're paying by the tonne, wet material costs more for the same volume.
- Ordering too little. A second small delivery costs more per cubic metre, and the colour of a second batch of gravel or sand may not match the first.
You can't return a pile of gravel. Order too little and you'll pay for a second delivery. Order too much and you've paid for stone you don't need. A few minutes with the calculator keeps you close to the right number.
Related tools
Frequently asked questions
How do I calculate how much gravel I need?
Multiply the length by the width by the depth, all in metres, to get cubic metres. A 5 m by 2 m path covered 50 mm (0.05 m) deep needs 5 × 2 × 0.05 = 0.5 m³. Multiply by the density of the material to get the weight (gravel is about 1.6 tonnes per cubic metre, so 0.5 m³ is about 0.8 tonnes) and add 5 to 10 percent for settling and waste.
How many tonnes are in a cubic metre of gravel, sand or soil?
Gravel and building sand are about 1.6 tonnes per cubic metre, crusher run is about 1.9, topsoil about 1.4, compost about 0.6 and bark chips about 0.35. Wet material is heavier and these figures can vary by around 15 percent, so confirm with your supplier.
What depth of gravel should I use?
A decorative gravel top layer is usually 25 to 50 mm. A driveway or load-bearing base is 100 to 150 mm of compacted crusher run, and a flower bed of topsoil is 100 to 150 mm. Mulch is normally spread 50 to 75 mm deep.
How much area does one cubic metre cover?
At 25 mm deep one cubic metre covers 40 m², at 50 mm deep 20 m², at 75 mm deep about 13 m², and at 100 mm deep 10 m². At 150 mm deep it covers about 6.7 m².
Should I add extra for compaction and waste?
Yes. Loose material settles and compacts, and a little is lost in spreading. Adding 5 to 10 percent is typical, and up to 20 percent for a compacted base such as crusher run under paving.