Crushed Stone Calculator

Background.

Crushed stone is sold by weight and laid by volume, and most ordering mistakes happen in the conversion between the two. The quarry or builders' merchant quotes per tonne; the drawing says a patch 6 metres by 3 metres needs 100 mm of compacted base. Getting from one to the other takes three things: the volume of the finished layer, an allowance for the stone that disappears into compaction, spillage and an uneven subgrade, and the bulk density of the particular product being delivered.

Bulk density is the figure that does the most damage when guessed. A heap of crushed stone is partly air, the gaps between angular fragments, so a cubic metre of it weighs far less than solid rock, which for granite is about 2,700 kg/m³. How much less depends on the grading, the moisture and whether the stone is loose in a lorry bed or rolled tight in place. ASTM C29, the standard test for aggregate bulk density, has both a loose (shovelled) procedure and compacted (rodded or jigged) ones precisely because the two give different answers. The 1,600 kg/m³ default is a placeholder, not a property of crushed stone in general: replace it with your supplier's figure for the product you are buying.

The allowance has to match the density you use. With a loose density, it must cover the volume lost when the layer is plated or rolled as well as waste. With a compacted density, it only needs to cover spillage and trimming.

The tonnage is a quantity to order against, not a delivery ticket. Suppliers round to their own load sizes and minimum orders, and some sell by the cubic yard or the short ton.

What is crushed stone calculator?

The order mass is the weight of crushed stone to buy so that, once spread and compacted, it fills a rectangular area to a stated depth. It is the compacted volume (length × width × compacted depth), enlarged by a percentage allowance and then multiplied by a bulk density: the mass of stone per cubic metre of space it occupies, with the voids between particles counted in. Because bulk density belongs to a specific graded product in a specific state rather than to rock in general, the page asks you for it instead of looking one up from a material name.

How to use this calculator.

1. 01Measure the length and width of the area in metres. For an L-shaped or irregular area, split it into rectangles, run each one and add the tonnages.
2. 02Enter the compacted depth, meaning the thickness of the finished layer after rolling rather than the loose depth before it. A 100 mm base is entered as 0.1.
3. 03Replace the bulk density with your supplier's figure for the exact product (a 20 mm clean stone and a graded sub-base are not the same), and find out whether it is a loose or a compacted density.
4. 04Set the allowance: with a loose density, make it large enough to cover compaction as well as waste; with a compacted density, a smaller margin for spillage and low spots in the subgrade will do.
5. 05Order on the tonnes figure, rounding up to the supplier's load size, and keep the order volume to hand in case they sell by the cubic metre.

The formula.

The calculation runs in three steps. First the compacted volume, V = L × W × D, in cubic metres. Second the order volume, V_order = V × (1 + a/100), where a is the waste and compaction allowance in percent. Third the mass, M = V_order × ρ ÷ 1,000, where ρ is the bulk density in kg/m³ and dividing by 1,000 turns kilograms into metric tonnes. Every term is a plain multiplier, so a 10% error in any one of them becomes a 10% error in the tonnage. Depth and density are the two to watch. Depth, because 50 mm extra on a 100 mm layer is a 50% increase that is easy to overlook when the base is being levelled. Density, because differences in grading and moisture between products are real and cannot be judged by eye. Nothing in the formula follows the shape of the ground under the layer; if the subgrade dips, raise the allowance to cover it.

A worked example.

Frequently asked questions.

References& sources.

1. [1]ASTM International. ASTM C29/C29M. Bulk density and voids in aggregate (PAYWALL). Retrieved 2026-08-06. access: gated.
2. [2]National Institute of Standards and Technology. NIST SI Guide, 2008 edition. Appendix B unit relationships. Retrieved 2026-08-06.
3. [3]International Code Council. 2021 International Residential Code. Building construction context. Retrieved 2026-08-06.