Bulk Material Weight Calculator
Converts between weight and volume for loose building and garden materials. Use it when the yard quotes by the tonne and you worked in cubic yards, or the other way round.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
weight = volume × bulk density volume = weight ÷ bulk density
Bulk density is the weight of a cubic metre of the material loose, with the air between the pieces counted in. It is not the density of the rock itself — solid granite is about 2,700 kg/m³, but crushed and tipped into a heap the same stone measures nearer 1,600, because a third of the heap is gaps.
What to watch out for
Every quote involves one of these conversions, and the density is where it goes wrong:
- Bulk density counts the gaps. A tonne of gravel is about 0.65 m³ because roughly a third of the pile is air. Using the density of the rock itself will put you out by half.
- Water is heavy. Aggregate delivered after a wet week can weigh 10–15% more per cubic metre. Buying by weight, that is material you paid for and did not get.
- Compacted is not loose. Sub-base measured in the ground is denser than the same stuff on the lorry. The figures here are loose and as delivered.
Frequently Asked Questions
How many tonnes is a cubic metre of gravel?
About 1.55 tonnes loose. A cubic yard is around 1.19 tonnes, since a cubic yard is 0.765 cubic metres.
How many cubic yards is a tonne of gravel?
Roughly 0.85 cubic yards, or 0.65 cubic metres. Denser materials give you less: a tonne of MOT Type 1 sub-base is only about 0.48 m³.
Why is bulk density lower than the density of the rock?
Because the gaps between the pieces are included. Solid limestone is around 2,700 kg/m³, but crushed and tipped into a heap it measures about 1,600 — the missing third is air.