Stone to KG Converter

Convert stone (st) to kilograms (kg) and kilograms back to stone using the official international definition: 1 stone = 6.35029318 kg.

1 stone = 14 pounds (lb) — traditional British unit
SI base unit of mass
? 9 st (typical adult)
?️ 12 st (athletic build)
? 15 st (heavy cargo reference)
? 5 st (child weight)
? 70 kg (≈ 11.02 st)
⚕️ 85 kg (≈ 13.38 st)
Current: 10 st = 63.5029 kg
Official conversion formula
1 stone (st) = 6.35029318 kilograms (exact, based on the international pound definition).
kg = stone × 6.35029318   |   stone = kg ÷ 6.35029318
Privacy first: All conversions are performed locally in your browser – no data leaves your device.

The stone: a British legacy unit explained

The stone (st) is a unit of mass equal to 14 pounds avoirdupois (about 6.35 kg). It originated in medieval Europe as a standard for wool and other commodities, but today it survives almost exclusively in the United Kingdom and Ireland for measuring human body weight. Unlike the metric system, the stone provides a convenient “mid‑scale” unit – one stone is roughly 6.35 kg, making it easier to express moderate weight changes (e.g., “I lost half a stone” = ~3.18 kg). Since 1985, the stone has been legally defined as exactly 6.35029318 kg, aligning with the international pound definition.

Historical relevance: The stone varied by commodity and region until the 19th century. The British Weights and Measures Act of 1835 standardized the stone at 14 pounds for trade. Today, the stone remains a culturally embedded unit in the UK for body weight – doctors, fitness apps, and personal scales often provide dual stone/kg readings.
Quick reference (stone → kg)
1 st = 6.350 kg
5 st = 31.751 kg
10 st = 63.503 kg
12 st = 76.204 kg
15 st = 95.254 kg
20 st = 127.006 kg
Quick reference (kg → stone)
50 kg ≈ 7.87 st
60 kg ≈ 9.45 st
70 kg ≈ 11.02 st
80 kg ≈ 12.60 st
90 kg ≈ 14.17 st
100 kg ≈ 15.75 st
Cultural note: In everyday speech, people might say "I weigh 11 stone 6 pounds", but in written form it is often abbreviated as 11st 6lbs or converted to a decimal stone value (11.43 st) for calculation.

How to use the stone–kg converter

  • Enter stone value: kilograms update instantly using the exact factor 6.35029318.
  • Enter kilograms value: stone recalculates automatically (bidirectional).
  • Click example pills: Quickly load common body weights or reference values.
  • Copy result: Use the copy button or the copy icon next to the live result to share or save the kilogram equivalent.
Case study: medical weight tracking in the UK

In UK general practice, patient weight is often recorded in stone and pounds, while medication dosages (e.g., paracetamol for children) are calculated in mg per kg. A patient weighs 11 st 6 lb. First, convert total stone: 11 st + (6 lb ÷ 14) = 11.4286 st. Then convert to kg: 11.4286 × 6.35029318 = 72.58 kg. Our calculator does this instantly – reducing medication errors and improving clinical safety. Similarly, fitness apps that synchronise with smart scales (kg) can convert historical stone readings to metric for trend analysis.

Mathematical foundation and precision

Since 1 lb = 0.45359237 kg exactly, and 1 st = 14 lb, we derive:

1 st = 14 × 0.45359237 = 6.35029318 kg (exact).

The reciprocal factor: 1 kg = 1 / 6.35029318 ≈ 0.15747304441777 st. Our converter uses double-precision arithmetic, providing at least 10 significant digits – sufficient for medical, scientific, and everyday use.

? Independent Verification

To ensure absolute transparency, you can independently verify our core formula:

  • 1 international pound (lb) = 0.45359237 kilograms (kg) [as defined by NIST]
  • 1 stone (st) = 14 pounds (lb)
  • Therefore: 1 st = 14 × 0.45359237 = 6.35029318 kg

You can replicate this calculation with any standard scientific calculator. All conversions in this tool are based on this unchangeable international standard.

Real‑world applications across domains

Healthcare & fitness

Body weight, BMI calculation, weight loss/gain tracking. Many UK gyms and diet plans still refer to stone.

Agriculture & livestock

Historically used for wool, meat, and produce. Some traditional markets still quote stone.

Education & history

Teaching imperial‑metric conversion, understanding old documents, or antique trade records.

Authority and definition references

The stone’s exact value derives from the international pound definition, which is overseen by the International Bureau of Weights and Measures (BIPM) and the National Institute of Standards and Technology (NIST). The UK’s Weights and Measures Act 1985 legally defined the stone as 6.35029318 kg for trade. Our converter follows these primary sources, ensuring full legal and metrological compliance.


Frequently Asked Questions

Because 1 stone = 14 pounds, and 1 pound = 0.45359237 kg exactly (international agreement 1959). Multiplying gives the exact stone value.

Primarily the United Kingdom and Ireland for body weight. It is also understood in Commonwealth countries but not commonly used for official trade.

Convert the pounds to stone (4 lb ÷ 14 = 0.2857 st). Add to the stone: 10.2857 st × 6.35029318 = 65.32 kg. Or use our advanced weight converter suite (coming soon).

Rarely. Some traditional recipes for large‑scale food production (cheese, meat) may reference stone, but most industries have metricated.

Accuracy to 6 decimal places (sub‑gram). For clinical dosing, it is more than sufficient – standard medical scales are accurate to ±0.1 kg.

The UK officially adopted the metric system for trade and official purposes, but the stone remains in common use for body weight due to cultural habit and tradition. The stone provides a convenient mid-scale unit for human weight (one stone is roughly 6.35 kg), making it easier to express weight changes (e.g., "I lost half a stone"). It is still taught and used in everyday life, especially in healthcare and fitness.

Convert the pounds to a decimal fraction of a stone by dividing by 14 (6 ÷ 14 ≈ 0.4286), then add to the stone value (11 + 0.4286 = 11.4286 st). Enter 11.4286 in the stone field. Our tool will then compute the equivalent in kilograms. For convenience, we are planning to launch an advanced weight converter that accepts combined stone and pounds input in the future.
References: NIST – SI Mass · BIPM SI Brochure · UK Weights and Measures Act 1985