Limestone Calculator

Background.

Crushed limestone is one of the cheapest ways to build a firm surface — a driveway, a footpath, a shed base, the sub-base under paving slabs. Quarries sell it by weight, but the job is measured in metres, so the practical question when ordering is how many tonnes the space will swallow.

Three things decide it. The first is plain geometry: the area times the finished, compacted thickness. The second is how much more stone has to arrive than that geometric volume, because some is pressed into soft ground, some is spilled at the edges and, above all, the layer shrinks when a plate compactor or roller goes over it. The third is bulk density — what one cubic metre of crushed limestone weighs, air gaps included.

That last figure is where estimates usually go wrong. Calcite, the mineral most limestone is made of, has a density of about 2,710 kg/m³, but a heap of broken stone is full of voids, so a cubic metre of it weighs far less. A value around 1,500 kg/m³, the default here, is a common working figure for loose crushed stone. Grades that include fines fill those gaps and weigh more per cubic metre than clean single-size chippings, and damp stock weighs more than dry. A supplier can usually give you the figure for each product, and it is worth asking before you order.

Depth has the most leverage of all. Moving from a 100 mm layer to 150 mm adds half again to the tonnage, so measure the dig rather than guessing it.

One scope note: this converts a layer of stone into tonnes. It does not work out spreading rates for garden or agricultural lime, which is applied per square metre to change soil pH.

What is limestone calculator?

The result is the mass of crushed limestone to order, in metric tonnes, for a rectangular layer of a chosen compacted thickness. It starts from the finished volume of the layer, enlarges it by a percentage allowance for compaction, settlement into the ground below and handling loss, and multiplies by the stone's bulk density — the mass of a cubic metre of aggregate including the spaces between particles, which is the property the ASTM C29 test method measures.

How to use this calculator.

1. 01Measure the length and width of the area in metres. For an L-shaped drive or a curved path, split it into rectangles and run each one, or work out the total area yourself and enter it as the length with a width of 1.
2. 02Enter the compacted depth — the thickness you want once the stone has been rolled or plate-compacted — in metres: 75 mm is 0.075 and 150 mm is 0.15.
3. 03Replace the 1,500 kg/m³ default with your supplier's bulk density for the exact product, and ask whether that figure is loose or compacted.
4. 04Set the allowance. With a loose density it has to cover the shrinkage from compaction as well as spillage and soft spots; with a compacted density it only needs to cover the losses.
5. 05Order the tonnes shown, rounded up to the supplier's load size, or use the order volume if the yard sells by the cubic metre.

The formula.

Order mass (t) = L × W × D × (1 + a ÷ 100) × ρ ÷ 1,000. L, W and D are the length, width and compacted depth in metres, so their product is the finished volume of the layer in cubic metres. The allowance a is a percentage that scales this up to the volume you need delivered — 8% turns 1 m³ into 1.08 m³. Multiplying by the bulk density ρ in kg/m³ gives kilograms, and dividing by 1,000 gives metric tonnes. Every term is a straight multiplier, so a 10% error in depth, area or density becomes a 10% error in the order. Depth and density are the ones people get wrong: an extra 25 mm on a 100 mm layer adds 25%, and two products from the same quarry can differ noticeably in bulk density. No density is looked up from the word limestone — the figure you type is the one used.

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.