How much gravel do I need?
Last reviewed 1 July 2026
Short answer
Multiply the area by the finished depth to get a volume, then multiply the volume by the material's bulk density to get a weight. A 20 m² path at 50 mm deep is 1 m³, which at 1,600 kg/m³ is 1.6 tonnes — about two UK bulk bags. If the layer will be compacted, order roughly 30% more than the finished depth suggests.
Work it out for your project with the gravel calculator →
The calculation in three steps
- Area. Length × width for a rectangle. Split awkward shapes into rectangles, triangles and circles and add them up.
- Volume. Area × finished depth. Keep the depth in the same units — 50 mm is 0.05 m, not 50.
- Weight. Volume × bulk density. Most gravels are 1,500–1,700 kg/m³, so 1,600 is a reasonable working figure.
weight (kg) = area (m²) × depth (m) × density (kg/m³)
Worked examples
| Job | Area | Depth | Volume | Weight | UK bulk bags (850 kg) |
|---|---|---|---|---|---|
| Border | 6 m² | 40 mm | 0.24 m³ | 384 kg | 1 |
| Path | 20 m² | 50 mm | 1.00 m³ | 1.6 t | 2 |
| Small drive | 40 m² | 75 mm | 3.00 m³ | 4.8 t | 6 |
| Large drive | 80 m² | 75 mm | 6.00 m³ | 9.6 t | 12 (order loose) |
Above about six bulk bags, a loose tipped load is usually cheaper — if you have somewhere to tip it.
Compaction: the step people miss
A decorative gravel layer is not compacted, so the volume you order is the volume you get. A sub-base is different. Granular material like MOT Type 1 loses roughly a quarter to a third of its loose volume when it is whacked down.
That means a 100 mm compacted sub-base needs about 130 mm of loose material. If you order for the finished depth you will be roughly 30% short — which on a 40 m² driveway is close to two tonnes.
The compaction factor is not the same for every material. Dense graded sub-base is around 1.3, angular chippings around 1.1, and rounded decorative gravel is effectively 1.0 because it is never compacted.
Important: Compact in layers
Ordering: bags, bulk bags or loose
| Quantity | UK | US |
|---|---|---|
| Under about 200 kg | Handy bags (25 kg) | Bagged (0.5 ft³) |
| 200 kg to 4 tonnes | Bulk bags (approx. 850 kg) | Bulk bags or bulk delivery |
| Over 4 tonnes | Loose tipped by the tonne | Bulk delivery by the cubic yard or ton |
UK bulk bags are sold as 'one tonne bags' but are usually filled to 800–900 kg. Ask before you order by the bag.
Things that shift the answer
- Moisture. A wet load can be 10% heavier than a dry one for the same volume. If you are buying by weight you get less material.
- Grading. A well-graded material with a range of particle sizes packs denser than a single-size one.
- Edge losses. Gravel migrates. Without edging you will be topping up within a year.
- Depth creep. People almost always end up laying deeper than they planned. Measure the finished level with a string line.
Related questions
- How many square metres does a tonne of gravel cover?
- At 1,600 kg/m³ and 50 mm deep, one tonne covers about 12.5 m². At 40 mm it covers about 15.6 m², and at 75 mm about 8.3 m². Divide 1,000 by (density × depth in metres) for any combination.
- Should I order extra?
- Yes, 5–10%. Aggregate is cheap relative to a second delivery charge, and running short in the middle of spreading a driveway is a bad afternoon.
Safety notice: Material planning only