How this calculator works
Area times depth gives the loose volume of gravel. Bulk density then converts volume to mass, which is the unit a pit or quarry usually sells. Pea gravel is a rounded, washed product around 5 to 10 mm across, and it packs to roughly 1500 to 1700 kg per cubic metre depending on moisture and compaction, so the density reference matters more than it does for crushed stone. Half-cubic-foot landscape bags hold about 20 to 23 kg, and the bag count uses that volume, not the bag weight printed on the outside.
Formula
Net volume = area x depth; order volume = net volume x (1 + waste); mass = order volume x bulk density; bags = ceil(order volume / 0.01416 m3); cost = mass in tonnes x price per tonne, or order volume x price per cubic metre, plus delivery.
Worked example
A 5 by 4 m bed at 50 mm deep holds 1.0 m3 of pea gravel. At 1600 kg/m3 that is 1600 kg, or 1.6 tonnes, and about 71 half-cubic-foot bags. With 10% waste the order rises to 1.1 m3 and 1760 kg.
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Frequently asked questions
How deep should pea gravel be?
About 50 mm for a decorative bed or path top dressing, and 75 to 100 mm where it is walked or driven on. Deeper layers need edging to stop the rounded stones spreading.
Is a tonne the same as a ton?
No. A metric tonne is 1000 kg, while a US short ton is 907 kg. The volume and bag figures do not change, but the price per unit does, so match the price basis to the supplier scale.
Why is pea gravel sold by volume as well as mass?
Because its bulk density changes with moisture and how it was loaded. A supplier quoting by the cubic metre is selling a measure of the pile, and the mass is an estimate; check the weight ticket if you are paying by the tonne.