Gravel Calculator
Enter your area and depth in millimetres to see how many cubic metres and tonnes of aggregate, MOT Type 1 sub-base and decorative shingle you need, and what it should cost in GBP.
Formulas shown on this page · Last reviewed October 2026
How the gravel calculator works
volume (m³) = length (m) × width (m) × depth (mm) ÷ 1,000
tonnes = volume × (1 + extra) × density (t/m³)
Gravel is sold by weight, so the calculator multiplies volume by an approximate loose density. Crushed rock and base materials are roughly 1.6 t/m³ and rounded decorative stone about 1.5 t/m³, but moisture and grading change this – ask your supplier for their figure and edit the density above. The default extra of 10% allows for compaction and uneven ground.
Typical gravel depths
| Use | Depth |
|---|---|
| Decorative gravel on a garden path | 40–50 mm |
| Gravel driveway surface | 50–75 mm |
| MOT Type 1 sub-base, compacted (75–150 mm under patios and driveways) | 100–150 mm |
| Drainage trench or French drain | Fill to trench depth |
Buying gravel in the UK
Builders’ merchants sell loose aggregate by the tonne and in bulk bags of roughly 850 kg, which are easier to deliver down narrow drives and through side gates. Popular choices include aggregate, MOT Type 1 sub-base and decorative shingle. With frequent rain, a well-compacted MOT Type 1 sub-base is what stops a patio or drive sinking – use a membrane under decorative gravel to limit weeds.
Bulk bags are weighed in kilograms, so the calculator rounds up to whole bags of the size you enter. Check the weight on the bag, because it varies by supplier.
At the default price of £38 per tonne for mot type 1 sub-base, one cubic metre (about 1.6 tonnes) costs roughly £60.80. These are typical prices – check your local supplier, as delivery charges and minimum loads vary by region.
Frequently asked questions
How much gravel do I need for a 5 × 3 m area at 75 mm deep?
The base volume is 1.125 m³. Adding 10% gives 1.24 m³, which is about 1.98 tonnes at 1.6 t/m³.
How many tonnes of gravel are in a cubic metre?
Roughly 1.5–1.6 tonnes for most crushed and decorative gravel, so 1.6 t/m³ is used as the default here. The exact figure depends on the material and moisture.
How many bulk bags of gravel do I need?
A bulk bag holds about 850 kg, so 1.98 tonnes needs 3 bags (rounded up). At £45 a bag that is £135.
How much extra gravel should I add?
Around 10% is a sensible allowance for compaction, uneven ground and spillage. Add more under pavers or driveways where the base is compacted hard.