Material
Area and depth
| Volume | Amount |
|---|
Buying it
| Bulk bags | 0 |
| 25kg bags | 0 |
How this calculator works
Volume is simply area × depth, with the depth converted from millimetres to metres before multiplying. That volume becomes a weight using the material's bulk density, the tonnes packed into each cubic metre, which varies by material because particle size, shape and moisture content all change how tightly it packs. Wastage on top covers compaction settling, spillage, and the reality that a tipped or bagged load rarely spreads perfectly evenly.
Why bulk density varies
The defaults here (gravel 1.6, sharp sand 1.7, loose topsoil 1.4, hardcore 1.9 tonnes per cubic metre) are typical figures used by builders' merchants, but actual density depends on moisture content, particle grading and how settled the material is. Damp sand is heavier than the same sand bone dry; compacted hardcore is considerably denser than the same stone loosely tipped. If your supplier quotes a specific density for the exact product you're buying, use that instead of the default.
Bulk bags versus 25kg bags versus loose tipped
For anything beyond a small job, a loose tipped load by the tonne is the cheapest way to buy aggregate, provided a delivery lorry can get access. Bulk bags (sometimes called jumbo or builder's bags) are the middle ground: no vehicle access needed beyond a spot to drop the bag, and a typical bag holds around 0.85 tonnes of usable material once you allow for what's left in the corners. 25kg bags are the most expensive per tonne by a wide margin and really only make sense for small top-ups or where nothing else will fit through the access you've got.
What this calculator does not check
This tool gives you a weight and a bag count, not a specification. It doesn't check whether your project needs a particular grading (for example, a sub-base needs a graded, compactable stone like MOT Type 1, not loose decorative gravel), whether the material needs compacting in layers rather than one deep pour, or whether you need a weed membrane or edging to contain it.
Related tools
Buying ballast to mix your own concrete rather than aggregate for a sub-base? The concrete calculator works that out directly. Need sand for mortar rather than a loose sub-base? See the brick and block calculator. Levelling ground before laying turf, in smaller quantities than a full sub-base job? The turf calculator covers topsoil top-ups alongside the turf itself.