Stones to Kilograms Converter

How Stones to Kilograms Conversion Works

A stone is a unit of weight equal to 14 pounds or approximately 6.35029 kilograms. It is used primarily in the United Kingdom and Ireland for measuring personal body weight. The stone-to-kilogram conversion is essential for anyone who needs to communicate their weight internationally, fill out medical forms in metric units, or use fitness apps that default to kilograms.

According to the UK Weights and Measures Act 1985, the stone was formally removed from official UK trade measurements in favor of metric units. However, a YouGov survey found that approximately 65% of British adults still describe their personal weight in stones and pounds. The NHS accepts both units on its official BMI calculator, reflecting this cultural reality.

The kilogram is the SI base unit of mass, used by over 95% of the world's population for everyday weight measurement. Understanding how to convert between stones and kilograms is particularly important for UK residents using international health services, importing fitness equipment with metric scales, or comparing their weight with global health statistics. Our BMI Calculator accepts both units for easy health assessment.

The Stones to Kilograms Formula

The conversion formula is:

Kilograms = Stones x 6.35029

For stones and pounds together:

Kilograms = (Stones x 14 + Pounds) x 0.45359

This derives from the exact definition: 1 pound = 0.45359237 kg, as established by the 1959 International Yard and Pound Agreement between the US, UK, Canada, Australia, New Zealand, and South Africa. Since 1 stone = 14 pounds: 14 x 0.45359237 = 6.35029318 kg exactly.

Worked example: Convert 11 stone 7 pounds to kilograms. Total pounds = (11 x 14) + 7 = 161 lbs. Kilograms = 161 x 0.45359 = 73.03 kg. Quick check: 11 x 6.35 = 69.85, plus 7 x 0.4536 = 3.18, total = 73.03 kg.

Key Terms You Should Know

• Stone (st) -- A unit of weight equal to 14 pounds (6.35029 kg). Used primarily in the UK and Ireland for personal body weight. Not commonly used in the US or continental Europe.
• Kilogram (kg) -- The SI base unit of mass, defined since 2019 by the Planck constant. Used by the vast majority of the world for everyday weight measurement.
• Pound (lb) -- A unit of weight equal to 0.45359237 kg. There are 14 pounds in a stone and 2.20462 pounds in a kilogram.
• Body Mass Index (BMI) -- A measure calculated as weight (kg) divided by height squared (m). A healthy BMI range is 18.5-24.9 according to the NHS and WHO.
• Imperial System -- The measurement system using stones, pounds, and ounces for weight. The UK uses a hybrid of imperial and metric units in daily life.

Stones to Kilograms Reference Table

This table covers the typical range of adult body weights. All values are calculated using the exact conversion factor of 6.35029318 kg per stone, as defined by NIST.

Practical Examples

UK resident visiting a doctor abroad: A British woman weighs 9 stone 10 pounds and needs to provide her weight in kilograms for a medical appointment in Spain. Conversion: (9 x 14) + 10 = 136 lbs. Then 136 x 0.4536 = 61.7 kg. She can use this value on the medical form and for any medication dosing calculations.

Fitness tracking: A man tracking his weight loss sees he has gone from 14 stone 3 pounds to 12 stone 11 pounds. In kilograms: start weight = (14 x 14 + 3) x 0.4536 = 90.3 kg, current weight = (12 x 14 + 11) x 0.4536 = 81.2 kg. Total loss: 9.1 kg. Use our Calorie Calculator to determine the daily caloric deficit needed for continued progress.

NHS BMI check: According to NHS guidelines, a healthy BMI is 18.5 to 24.9. A man who is 5 feet 10 inches tall and weighs 12 stone 6 pounds: weight = (12 x 14 + 6) x 0.4536 = 79.0 kg, height = 1.778 m. BMI = 79.0 / (1.778 x 1.778) = 25.0 -- right at the boundary between healthy and overweight. Our BMI Calculator performs this calculation automatically.

Tips for Converting Between Stones and Kilograms

• Quick mental math -- multiply by 6.35: For a rough estimate, multiply stones by 6 and add a third of the stone value. For example, 10 stone: 10 x 6 = 60, plus 10/3 = 3.3, total = 63.3 kg (exact: 63.50 kg). This gets you within 0.5% accuracy.
• Remember that 1 stone = 14 pounds, not 10 or 16: A common mistake is assuming stones follow a decimal or hexadecimal pattern. The 14-pound definition dates to the medieval wool trade and has remained unchanged since the Weights and Measures Act of 1835.
• UK digital scales often show both units: Most bathroom scales sold in the UK allow switching between stones/pounds, kilograms, and pounds-only. Set your scale to kilograms to become familiar with metric body weight over time.
• Use our Weight Converter for other units: If you need to convert stones to pounds, ounces, grams, or metric tons, our comprehensive weight converter handles all standard weight units simultaneously.
• Medical context matters: Hospitals and pharmacies in the UK increasingly use kilograms exclusively for drug dosing to prevent errors. If asked your weight in a medical setting, have your kilogram equivalent ready.

History of the Stone as a Unit of Weight

The stone has a long history in the British Isles. Before standardization, the stone varied by commodity and region -- a stone of wool weighed 14 pounds, but a stone of butcher's meat was 8 pounds, and a stone of glass was 5 pounds. The Weights and Measures Act of 1835 standardized the stone at exactly 14 avoirdupois pounds for all purposes.

According to the International Bureau of Weights and Measures (BIPM), the stone is not part of the International System of Units (SI) and is classified as a non-SI unit. The EU Directive 80/181/EEC prohibited its use in trade within EU member states, though the UK's departure from the EU has not led to any formal return of the stone for commercial purposes. The stone persists purely as a cultural convention for personal body weight in the UK and Ireland, with no legal status in commerce.