Gravel Calculator

Gravel is sold by weight, but you measure the area and depth. Multiply length by width by depth (in metres) for cubic metres, then multiply by the gravel density to get tonnes. Pea gravel runs at about 1.6 tonnes per cubic metre; MOT Type 1 sub-base is denser at 2.1. A 10 m by 5 m driveway laid 50 mm deep needs 2.5 cubic metres, which converts to roughly 4 tonnes of pea gravel before wastage.

The calculator handles this in one step and adds a 10% allowance, because gravel always settles, scatters and disappears down border edges. Bulk bags hold around 850 kg each (the trade calls them tonne bags but most are slightly under). On a typical 4-tonne driveway order, expect 5 bulk bags delivered. Mini-bags at 25 kg each are useful for top-ups and hard-to-access gardens, but at roughly £4 a bag they cost three times as much per tonne as bulk delivery.

A decorative top-up of 25 mm looks fine on a smart border. Anything you walk on regularly needs at least 50 mm to bed in properly without showing the membrane underneath. Driveways take a 50 mm finishing layer over a 100 to 150 mm sub-base of MOT Type 1, which is why a new driveway uses two different products and roughly four times the tonnage of a decorative scheme.

On the slope of a sloping garden, gravel migrates downhill. A retaining edge (timber or steel) keeps it in place and saves a top-up every spring. For the path edging and patio kerbs that often go alongside the gravel job, [Concrete Calculator](/concrete-calculator) handles the bedding mix.