Gravel calculator
At 50 mm deep, one tonne of gravel covers about 11.8 m², and a 20kg bag covers about 0.24 m².
- 20kg bags
- 64
- Bulk bags (850kg)
- 2
- Area
- 15.00 m²
- Volume
- 0.75 m³
5 × 3 m at 50 mm deep, using 1.7 tonnes per m³.
Bag counts are rounded up. Bulk bag weights vary by supplier, so check theirs.
How much gravel per square metre
Using 1.7 tonnes per m³. Find your depth to see what one bag or bulk bag covers.
| Depth | Gravel per m² | 20kg bag covers | Bulk bag covers | One tonne covers |
|---|---|---|---|---|
| 20 mm | 34 kg | 0.59 m² | 25.0 m² | 29.4 m² |
| 30 mm (borders) | 51 kg | 0.39 m² | 16.7 m² | 19.6 m² |
| 40 mm | 68 kg | 0.29 m² | 12.5 m² | 14.7 m² |
| 50 mm (paths, driveways) | 85 kg | 0.24 m² | 10.0 m² | 11.8 m² |
| 75 mm | 128 kg | 0.16 m² | 6.7 m² | 7.8 m² |
| 100 mm | 170 kg | 0.12 m² | 5.0 m² | 5.9 m² |
How we calculate this
We work out the volume of the space, then multiply by how much a cubic metre of gravel weighs. That gives the weight to order, which we then split into bags.
A cubic metre of gravel weighs about 1.68 tonnes. We round up to 1.7 tonnes, as most suppliers do, so you're less likely to run short. Some stone weighs more or less than this, so change the gravel weight if your supplier gives a figure.
Questions people ask
How deep should gravel be?
About 50 mm for paths and driveways, where people walk or drive on it, and about 30 mm for planted borders. Much deeper than that and gravel becomes hard to walk on and can shift about.
How much does a tonne of gravel cover?
About 11.8 m² at 50 mm deep, or 19.6 m² at 30 mm deep.
How many 20kg bags are in a bulk bag?
About 43 for an 850kg bulk bag. If you need more than about 21 small bags, a bulk bag usually works out cheaper and saves trips.
Do I need anything under the gravel?
For paths and borders, a weed membrane underneath stops weeds coming through and the gravel sinking into the soil. Driveways usually need a compacted sub-base first, so the gravel layer here is only the top surface.
Why do gravel calculators give different answers?
Mostly because they use different weights per cubic metre and different bulk bag sizes. Bulk bags are sold from about 800 kg to a full tonne. Check the bag weight with your supplier and enter their gravel weight if they give one.
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