Stone to tonnes:
multiply by 0.00635029

How many tonnes are in a stone?

One stone is 0.00635029318 metric tonnes. That is only about six thousandths of a tonne, since a stone weighs 6.35 kg and a tonne is 1,000 kg.

The stone is a British unit of 14 pounds. The metric tonne is 1,000 kilograms. Converting between them is a two-step idea compressed into one factor.

Stone is a unit that people use for single bodies, so the numbers rarely rise above a few hundred, while tonnes describe the weight of vehicles and cargo. Turning a stone figure into tonnes therefore usually means adding up a group, such as passengers on a boat, a team on a weighbridge or a collection of livestock. A single stone is about 6.35 kg, so even a hundred of them are only 0.635 tonnes. Seeing the answer as a small decimal is normal and not a sign of a mistake.

Stone to tonne formula and examples

A smaller case: 14 stone is 14 × 0.00635029318 = 0.0889 t, or about 88.9 kg. And a heavy load of 50 stone is 0.3175 t.

1. 1Write the weight in stone. Change any extra pounds into a fraction by dividing by 14.
2. 2Multiply by 0.00635029318.
3. 3Round to three or four decimals, since the answer is small.
4. 4Check by turning stone into kilograms (about 6.35 each) and dividing by 1,000.

Chart: stone to tonnes

Where stone to tonne matters

• Turning a total of many people's body weights, such as a ferry or lift load, from stone into tonnes.
• Reading older records of goods or livestock measured in stone and comparing them to modern tonnage.
• Writing reports where UK sources give stone and an international audience expects metric tonnes.
• Sports or charity events that count total weight lost or lifted across a group.

A charity event where 200 people each weigh about 12 stone totals 2,400 stone, which is about 15.24 tonnes.

Quick sanity checks for stone to tonnes

A thousand stone is 6.35 tonnes, so a hundred is 0.635 t and ten is 0.0635 t. Each step down shifts the decimal one place.

Try 30 stone: 30 × 0.00635029318 = 0.1905 t, which is about 190.5 kg. That fits 30 × 6.35 kg.

The tonne result should always look tiny next to the stone figure, because it is only about 0.6 percent of it.

Common mistakes when converting stone to tonnes

• Overestimating the size of a stone. It is only about 6.35 kg, so you need about 157 of them to reach one tonne.
• Using 14 instead of 6.35. 14 is the number of pounds in a stone, not the kilograms.
• Confusing the metric tonne with the long ton. The long ton is 160 stone, and the tonne is 157.47 stone.
• Dropping decimals too early. For 500 stone, 3.175 t becomes 3 t if you round too soon.