How this calculator works
Gravel and aggregates are sold by weight (tonnes) or by the bulk bag, but you measure the area and the depth. Multiply the area by the depth in metres to get cubic metres, add your waste allowance, and multiply by the weight of one cubic metre of the material to get tonnes.
Worked example: a 5 × 4 m gravel area (20 m²) at 50 mm deep, in 20 mm gravel at 1.6 tonnes per m³: 20 × 0.05 = 1 m³, which is 1.05 m³ with 5% extra, or 1.68 tonnes. That is three 0.8 tonne bulk bags. One tonne covers 12.5 m² at that depth.
How far does a tonne go? (20 mm gravel)
Square metres covered by one tonne at each depth.
| Depth | Area per tonne | Typical use |
|---|---|---|
| 30 mm | 20.8 m² | Decorative borders |
| 40 mm | 15.6 m² | Garden paths |
| 50 mm | 12.5 m² | Driveways and gravel gardens |
| 75 mm | 8.3 m² | Heavily used drives |
Tips before you buy
- For a drive or path, lay the gravel over a weed-control membrane and a compacted sub-base, with an edging to hold it in place. A gravel retention grid stops the stones moving and rutting.
- Use angular crushed stone for a base, because it locks together. Rounded gravel and chippings are decorative and move underfoot.
- Order a bulk bag, or a loose load on a tipper truck for bigger areas, and check the delivery access and where it will be placed. A full bulk bag is heavy and is dropped where the truck stops.
- Use the right depth: a thin layer shows the membrane, and a very thick layer is hard to walk on. 40 to 50 mm is right for most gravel paths and drives.
- In England, a gravel drive in a front garden is permeable, so it is fine without planning permission, but paving more than 5 m² with an impermeable surface is not.
Tools & materials for this project
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Frequently asked questions
How much gravel do I need for a 5m x 4m area?
At 50 mm deep, 1.05 m³ with 5% extra, which is about 1.7 tonnes of 20 mm gravel, or three bulk bags.
How many tonnes of gravel per cubic metre?
About 1.6 tonnes for 20 mm gravel, 1.5 for slate chippings, and around 1.7 for sharp sand. The supplier's figure is best.
How many bulk bags of gravel do I need?
Divide the tonnes by the size of the bag, about 0.8 tonnes, and round up. A bulk bag covers about 10 m² at 50 mm.
How deep should a gravel drive be?
40 to 50 mm of gravel on top of a compacted sub-base of at least 100 mm of MOT Type 1, over a membrane.
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Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.