Gravel Calculator
Gravel is sold by weight, in bulk bags of roughly 850 kg or small bags of 20 to 25 kg, but you measure the job by area and depth. This calculator converts the volume to weight using the bulk density of the material you choose, adds a compaction allowance for sub-base, and rounds up to whole bags.
Your measurements
Check your order
Your outdoor material order
- Mark the footprint and check finished levels, depth or board layout as applicable.
- Confirm sales units, delivery access and the supplier’s allowance for settlement or compaction where needed.
- Measure edging and finishing runs separately and check the tools you can reuse.
Tools for this job
Measure the footprint before delivery, then spread loose gravel to an even depth. Follow the base and compaction requirements for the intended use.
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- Spread loose ground materials
Garden rake
Fiskars Pro garden rake
For spreading loose soil or gravel and preparing an even surface. Raking distributes material; it does not replace any compaction the installation requires.
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Long tape measure
Komelon 6611 100-foot open-reel tape
For measuring longer outdoor runs and marking out areas. Keep the tape straight and use the same units throughout; this listing is for the 100-foot model.
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Already have suitable tools? Reuse them. These are optional product suggestions, not a complete equipment list or a hands-on comparison. Amazon may redirect Amazon.com links to local products or search results. Amazon.nl links search for alternatives, which may differ in brand, size and specification. Check suitability, seller, delivery and any import costs on your chosen store before ordering.
How much gravel do I need?
Gravel is a volume problem that ends in a weight. Measure the area, decide on the depth, and multiply to get the volume in cubic metres. Then convert to weight using the bulk density of the material, because suppliers sell by the bag, the bulk bag or the tonne, and a bulk bag holds a fixed weight, not a fixed volume. Loose gravel and shingle run about 1.6 tonnes per cubic metre, slate chippings are lighter at about 1.4, and crushed stone for a sub-base is heavier, especially once it is compacted.
Confirm the layer depth for the intended use and site before measuring the volume. A compacted sub-base needs a loose-material order that accounts for compaction. The calculator adds the percentage you select and rounds up to whole bags; the 20% preset is an ordering allowance, not a claim that every product loses 20% of its volume.
The formula
Bulk density of common aggregates
Densities vary with the stone, the grading and how wet it is, so treat these as planning figures and check the product listing, which usually quotes a coverage per bag at a given depth. Choose the custom option to enter your own density.
| Material | Bulk density | Weight per m² at 5 cm | One 850 kg bulk bag covers |
|---|---|---|---|
| Gravel, pea shingle (10 to 20 mm) | 1.5 to 1.6 t/m³ | 80 kg | about 10.5 m² |
| Decorative pebbles, cobbles (20 to 40 mm) | about 1.6 t/m³ | 80 kg | about 10.5 m² |
| Slate chippings | about 1.4 t/m³ | 70 kg | about 12 m² |
| Sharp sand | about 1.5 t/m³ | 75 kg | about 11 m² |
| MOT type 1, crushed stone sub-base | 1.75 t/m³ loose, 2.0 to 2.1 compacted | 88 kg loose, 105 compacted | about 8 m² compacted |
Worked example
A gravel area 6 × 4 m (20 × 13 ft) at 5 cm deep in 20 mm gravel. Area = 24 m². Volume = 24 × 0.05 = 1.2 m³. Weight = 1.2 × 1.6 t/m³ = 1.92 tonnes, or 1,920 kg. In 850 kg bulk bags that is 2.26 bags, so 3 bulk bags (2,550 kg) with a little over half a bag to spare; in 25 kg bags it would be 77.
A driveway base is a different order of magnitude. A 12 × 3 m drive at 15 cm of MOT type 1 is 5.4 m³ finished, 6.48 m³ with the 20% compaction allowance, and 6.48 × 1.75 = 11.34 tonnes: 14 bulk bags, or a loose tipper load of about 11.5 tonnes.
How deep should gravel be?
- Decorative path or border: 4 to 5 cm (1.5 to 2 in) over a weed membrane. Thinner shows the membrane; thicker is hard to walk on.
- Around plants or as a mulch: 5 cm (2 in), with the membrane cut around each stem.
- Gravel driveway surface: 10 cm (4 in) in total, laid as two 5 cm layers on a compacted sub-base. A single loose layer ruts and spreads under tyres; a gravel grid keeps it in place.
- Sub-base under a drive, patio or shed: 10 cm (4 in) of compacted MOT type 1 for a path or patio, 15 cm (6 in) for a driveway, compacted in layers of no more than 7.5 cm.
- French drain or soakaway: clean 20 mm stone with no fines, to the depth of the design; use the volume calculator for an odd shape.
Bulk bag, small bags or a loose load?
A bulk bag is filled by weight, usually 800 to 900 kg, and is sometimes called a tonne bag even though it is not. The volume inside depends on what is in it: about 0.53 m³ of gravel, 0.6 m³ of slate chippings, but only 0.43 m³ of compacted MOT type 1. That is why the calculator works in kilograms and lets you set the bag weight.
Small 20 or 25 kg bags make sense up to a couple of hundred kilograms, where you can carry them through the house. For a driveway sub-base, loose delivery by the tonne from a tipper is an option that needs somewhere to tip. Whatever the format, check the delivery: bulk bags are craned off a lorry onto a hard, level surface, and 850 kg on a lawn or a manhole cover is a problem.
What else the job needs
- Weed membrane under decorative gravel: the area plus about 10% for overlaps at the joints.
- Edging to stop the gravel migrating: measure the perimeter, or get it from the area calculator.
- A sub-base under any driveway or patio, calculated separately here with MOT type 1 and the 20% allowance, then the paving calculator for the slabs.
- Topsoil if you are also levelling beds. Use the volume calculator with Custom density and the supplier’s bag weight to convert a bed volume to bags. Check any settlement allowance separately.
- Concrete for any post or edging haunching: the concrete calculator.
Sources and assumptions
Volume is area × depth, with any selected allowance. Multiplying by bulk density converts volume to weight; bag quantities then round up from the selected bag weight.
- Long Rake Spar: aggregate planning questions: The producer explains that aggregate quantity depends on the project area, depth and chosen product, with a calculator and stockist advice for specific materials.
Before using this estimate
- The generic density presets are not quarry-specific measurements. Moisture, grading and compaction can change both coverage and delivered weight.
- Check whether the entered depth and supplier density refer to loose or compacted material; do not apply a compaction allowance twice. Bulk bags are not a universal weight.
Source notes reviewed . See how we check calculations and handle corrections.
Planning your order
Check the inputs before buying: measure the surfaces you need, then apply an allowance and round to whole packs. The guides include worked examples you can follow alongside this calculator.
Published by OrderEnough. This is a planning estimate: check the product specification and the assumptions above before ordering. Last updated . Read how we source our figures on the methodology page.