Gravel Calculator
Gravel is sold by weight but spread by volume, so every gravel order starts with a volume-to-weight conversion. This calculator does both: enter the area and layer depth, and get cubic metres, tonnes and bag counts.
Density is set to 1.5 t/m³ (1.4 tons/yd³), typical for crushed stone 20 mm (¾ in). Decorative pebbles and larger stone vary — check your supplier.
Enter valid values to see the results.
Formula
Depth must be converted to metres (5 cm = 0.05 m) or feet (2 in = 0.167 ft). Imperial volume in ft³ is divided by 27 to get cubic yards, then multiplied by 1.4 for short tons.
How to measure
- Measure the length and width of the area. For curved paths, measure the centreline length and average width.
- Choose depth by use: 5 cm (2 in) for paths, 10 cm (4 in) for driveways, 15 cm+ for heavy vehicles.
- If replacing old gravel, measure the depth you want to add, not the total.
Worked example
Practical tips
- Order in bulk (loose tonnes) above 1 tonne — bags cost 2–3 times more per tonne.
- Compact gravel in 5 cm layers with a plate compactor for driveways.
- Lay geotextile fabric under the gravel to stop it sinking into soil and weeds coming through.
- Angular crushed stone locks together and stays put; rounded pebbles migrate and need edging.
Waste allowance
Add 5–10% for compaction and uneven ground. Gravel compacts 10–15% under rollers, so a 10 cm loose layer finishes at about 8.5–9 cm.
Recommended gravel depth by application
| Application | Metric | Imperial |
|---|---|---|
| Garden path | 5 cm | 2 in |
| Patio base | 10 cm | 4 in |
| Driveway | 10–15 cm | 4–6 in |
| Drainage / French drain | 15–20 cm | 6–8 in |
Common mistakes
- 1 Ordering by area without depth — the same 24 m² needs 1.8 t at 5 cm but 5.4 t at 15 cm.
- 2 Forgetting compaction: loose gravel settles 10–15%, leaving the surface below the planned level.
- 3 Using path depth for a driveway — car wheels sink into a 5 cm layer within weeks.
- 4 Skipping geotextile on soft soil: gravel disappears into the ground within a season.
Frequently asked questions
How many tonnes of gravel per cubic metre?
About 1.5 tonnes per m³ for standard 20 mm crushed stone. Light decorative aggregates can be 1.2 t/m³, dense basalt up to 1.7 t/m³.
How much gravel do I need for a 10 m² path?
At 5 cm depth: 10 × 0.05 = 0.5 m³, about 0.75 tonnes. With 10% waste, order 0.8–0.9 tonnes or 33 bags of 25 kg.
How deep should gravel be for a driveway?
10–15 cm (4–6 in) over a compacted sub-base for cars. For heavy vehicles or soft ground, go to 20 cm with a coarser base layer underneath.
Is it cheaper to buy gravel in bags or bulk?
Bulk. A loose tonne typically costs the same as 10–15 bags of 25 kg (250–375 kg). Bags only make sense under ~500 kg or where a truck cannot deliver.
What area does 1 tonne of gravel cover?
About 13 m² at 5 cm depth, 6.5 m² at 10 cm, or 4.3 m² at 15 cm (at 1.5 t/m³ density).