The short answer
Multiply the length × width × depth in metres to get cubic metres, add about 10% for settling, then multiply by the material's density: roughly 1.6 tonnes per m³ for gravel. A 5 × 3 m area at 50 mm deep is 0.825 m³ with the extra, or about 1.3 tonnes, which is 2 bulk bags of 850 kg.
Try the Gravel CalculatorMeasure the area
Measure the length and width of the area in metres and multiply them to get square metres. For an L-shape or a curved border, split it into rectangles, work out each one and add them together. A circle is about 3.14 × the radius × the radius.
Measure the finished surface, not the hole, unless you are digging out. If you are replacing existing gravel, measure the depth you need to add, not the total depth.
Choose a depth
Decorative gravel on a path or border is often laid around 40–50 mm deep, which is enough to cover a weed membrane without being hard to walk on. Larger stones need a little more depth than fine pea shingle.
Driveways and paths that take regular traffic usually sit on a compacted sub-base, such as MOT Type 1, under the top layer. The right depths depend on the ground and the use, so follow your supplier's or installer's recommendation. Work out the top layer and the sub-base separately, because they have different densities.
Convert cubic metres to tonnes
Multiply length × width × depth, all in metres, to get the volume in cubic metres. A depth of 50 mm is 0.05 m. Then add about 10% for settling, compaction and uneven ground.
Most suppliers sell by weight, so multiply the volume by the material's density. Typical figures are about 1.6 tonnes per m³ for gravel and sharp sand, 2.1 for MOT Type 1 and 1.4 for topsoil, but they vary with moisture and stone size. Use your supplier's figure if they give one.
- 5 × 3 m area = 15 m²
- 15 m² × 0.05 m deep = 0.75 m³
- 0.75 m³ + 10% = 0.825 m³
- 0.825 m³ × 1.6 t/m³ = 1.32 tonnes
Turn tonnes into bags
Divide the weight by the bag size and round up. Bulk bags are often around 800–900 kg, so 1.32 tonnes is 2 bags of 850 kg. Small bags are usually 20–25 kg: the same job would need 53 bags of 25 kg, which is why bulk bags are usually better value for anything bigger than a small border.
Check where the bags can be delivered. Bulk bags are usually dropped by a crane lorry, so allow space at the kerb or driveway and plan how you will barrow the gravel to where it is needed.
This guide is general information to help you plan, not professional advice. Check product instructions and your supplier's guidance before you buy, and ask a qualified professional about structural or safety-related work. See our terms of use.