Gravel and Aggregate Calculator

How to use the gravel and aggregate calculator

1. Fill in the fields — they start with a worked example.
2. Read the answer, and the arithmetic shown beneath it.
3. Copy the results, or adjust the inputs to compare scenarios.

About this tool

Loose materials are ordered by weight but specified by depth, so the conversion runs through density — and density differs enough between materials to matter. Gravel is roughly 1.5 tonnes per cubic metre, sand about 1.6, topsoil closer to 1.3, and bark mulch only around 0.35. Using a gravel figure to order mulch overestimates by a factor of four.

Depth is where most of the judgement sits. Decorative gravel needs 40 to 50 mm to hide the membrane beneath it, and going deeper is not better — anything much over 50 mm becomes unpleasant to walk on and impossible to push a wheelbarrow through. A gravel driveway is different: it needs a sub-base beneath it, and the gravel layer alone is not the whole build-up.

Mulch works the opposite way. It needs 50 to 75 mm to suppress weeds at all, and a thin layer achieves nothing except looking tidy for one season.

Bulk bags hold about a cubic metre and are far cheaper per tonne than small bags. The crossover is around six or seven small bags, so the small-bag count is worth reading mainly as a signal to order bulk instead.

Common uses

• Ordering gravel for a path or driveway.
• Working out mulch for a border.
• Estimating topsoil for raised beds.

Frequently asked questions

How deep should gravel be?

40 to 50 mm for decorative gravel over a membrane. Deeper is harder to walk on, not better. A driveway needs a compacted sub-base beneath the gravel as well.

How deep should mulch be?

50 to 75 mm to suppress weeds. A thinner layer looks tidy briefly and does nothing useful.

Is a bulk bag cheaper than small bags?

Almost always, by a wide margin per tonne. The crossover is around six or seven small bags.