Gravel calculator
This gravel calculator shows how much gravel you need for an area: enter length, width and depth, then pick the material and an allowance. 5 m × 3 m at a depth of 10 cm plus 10% allowance is 1.65 m³, or about 2.8 tonnes of dry gravel.
Example: Length 5 m · Width 3 m · Depth (layer thickness) 10 cm · Material: Gravel, dry (1.68 t/m³) · Allowance for compaction and waste 10 % → Amount needed in tonnes: 2.77. Source: Engineering ToolBox – Dirt and Mud: Densities (gravel dry 1,680 kg/m³, wet 2,000 kg/m³; sand dry 1,555 kg/m³, wet 1,905 kg/m³). Updated: .
How it is calculated
Calculating gravel: the formula
Volume = length × width × depth (in meters). With allowance: volume × (1 + allowance ÷ 100). The weight follows from the bulk density: tonnes = volume × density.
- 5 m × 3 m × 0.10 m = 1.5 m³; with 10% allowance 1.65 m³
- Dry gravel (1.68 t/m³): 2.77 t – wet (2.00 t/m³): 3.30 t
- Dry sand (1.555 t/m³): 2.57 t
Why tonnes and cubic meters?
Suppliers sell gravel by the tonne (weighbridge) or by volume (bulk bag, load). Converting between them uses the bulk density, the weight of one cubic meter of loose material. It is lower than the density of the solid rock because there is air between the grains.
Dry or wet?
Wet gravel weighs clearly more than dry gravel: for the same area it is 3.30 instead of 2.77 tonnes here. The volume hardly changes. If you are charged by weight, moisture is worth keeping in mind.
Allowance
Loose material settles when it is spread and compacted, and some is lost. An allowance of 5–15% is common; the calculator assumes 10%, and you can change it.
Honest limits
The densities come from a general materials table (Engineering ToolBox) and apply to typical loose gravel and sand. Crushed stone, crusher sand or recycled aggregate can differ; use the own-density option for those. Sub-base and drainage layers have requirements from the designer or standards that the calculator does not know.
Frequently asked questions
How do I calculate how much gravel I need?
Length × width × depth gives the volume in m³; multiply by the allowance. 5 × 3 × 0.10 m is 1.5 m³, or 1.65 m³ with a 10% allowance.
How many tonnes are in a cubic meter of gravel?
Dry gravel weighs about 1.68 t per m³ and wet gravel about 2.0 t. The exact value depends on grain size and moisture.
How much gravel do I need for 10 m²?
At 10 cm depth, 1 m³, which is about 1.7 tonnes of dry gravel – plus allowance.
Does it work for crushed stone?
Yes, with “Own bulk density”: enter the density from the supplier’s data sheet.
Why add an allowance?
Loose material compacts as it is spread, and some is lost in transport. With 5–15% extra the order usually suffices.
Sources and legal basis
- Engineering ToolBox – Dirt and Mud: Densities (gravel dry 1,680 kg/m³, wet 2,000 kg/m³; sand dry 1,555 kg/m³, wet 1,905 kg/m³)
- BIPM – SI Brochure: tonne (1 t = 1,000 kg) as a unit accepted for use with the SI
As of: · Editorial policy
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