Stone weights and unit conversions

Volume to weight

There is no universal conversion from cubic yards to tons, because it depends on the material's bulk density. What is universal is the method: tons = cubic yards × tons per cubic yard, where the second figure comes from the product.

Most crushed aggregate falls between 1.3 and 1.5 tons per cubic yard. Sand is 1.3-1.4 dry and up to 1.6 wet. Topsoil is around 1.1-1.3. Lightweight decorative products like lava rock can be as low as 0.65.

Moisture matters more than people expect — a rain-soaked pile of sand can weigh 15% more than the same volume dry, which shows on the weighbridge ticket but not in the yard.

Which ton?

A US short ton is 2,000 lb (907 kg). A metric tonne is 1,000 kg (2,205 lb). A UK long ton is 2,240 lb (1,016 kg). Aggregate in the US is sold in short tons; in the UK and Europe, in metric tonnes.

The gap is about 10% between a short ton and a tonne — enough to short an order by a full truckload's worth on a big job if the units are mixed up.

The stone as a weight unit

In the UK and Ireland, a stone is a unit of body weight equal to 14 pounds, or 6.35 kg. It has nothing to do with aggregate, but it shares the word, which is why 'stone calculator' searches split between two completely different intents.

To convert: kilograms ÷ 6.35029 = stone. Pounds ÷ 14 = stone. Stone are conventionally written as stone-and-pounds, so 70 kg is 11 stone 0.2 lb — usually rounded to 11 st 0 lb.

• 1 stone = 14 lb = 6.35029 kg
• 1 short ton = 2,000 lb = 0.907 tonne
• 1 cubic yard = 0.7646 cubic metres
• 1 tonne per m³ = 0.843 tons per cubic yard

Metric aggregate maths

Working in metric: volume in cubic metres is area in m² times depth in metres. Multiply by bulk density in tonnes per cubic metre — typically 1.5-1.7 for crushed stone, 1.6 for sand — to get tonnes.

A 6 × 4 m patio base at 150 mm is 3.6 m³, about 5.8 tonnes of MOT Type 1 at 1.6 t/m³, before compaction allowance.