Before ordering driveway gravel, you need three measurements: the area to cover, the intended finished depth and the material’s bulk density. The same area can require very different weights depending on the aggregate and depth.
1. Measure the area
For a rectangular driveway, multiply its length by its width. For an irregular shape, divide it into smaller rectangles, calculate each area and add them together. Measure in metres so the result is in square metres (m²).
2. Convert the gravel depth to metres
Divide a depth in millimetres by 1,000. For example, 50 mm is 0.05 m. The suitable depth depends on whether the gravel is a decorative top layer or part of a properly designed driveway build-up. Gravel alone is not a substitute for a suitable load-bearing sub-base.
3. Calculate volume, then weight
Volume (m³) = length (m) × width (m) × depth (m). Add a sensible allowance for uneven ground and handling, then multiply by the supplier's stated bulk density in tonnes per cubic metre to estimate tonnes.
Worked example: a 5 m × 3 m area
- Area: 5 × 3 = 15 m².
- At 50 mm depth: 15 × 0.05 = 0.75 m³.
- With a 10% allowance: 0.75 × 1.10 = 0.825 m³.
- At an illustrative density of 1.6 t/m³: 0.825 × 1.6 = 1.32 tonnes.
- If the supplier sells genuine 800 kg bags, 1.32 ÷ 0.8 = 1.65, so round up to two bags.
These numbers are a buying estimate, not a recommended driveway specification. Check the aggregate grading, compacted depth, drainage, edging and sub-base with your supplier or installer.
Bulk bags or loose delivery?
Compare the total delivered cost, not just the advertised price per bag. Check the actual bag weight (a “bulk bag” does not always contain 800 kg), minimum loose-load quantities, delivery access and whether you can safely store excess material. If the supplier quotes cubic metres rather than tonnes, use that supplier's density rather than a generic conversion.
Common mistakes
- Confusing square metres (area) with cubic metres (volume).
- Using a decorative gravel depth as a structural driveway specification.
- Assuming all aggregate has the same density.
- Forgetting compacted thickness, waste, delivery charges and access.
Frequently asked questions
How many tonnes are in one cubic metre of gravel?
It varies by aggregate and moisture content. The 1.6 t/m³ figure above is only an example; ask your supplier for the relevant bulk density.
Can I use the same calculation for paths?
Yes, for estimating loose aggregate quantities. The required construction layers and depth may differ.
Calculate my gravel quantity →
Note: Illustrative UK planning estimates only. Follow product instructions and obtain qualified advice for structural work, drainage or site-specific conditions.