How to Convert Kilograms to Stones: The Complete Guide
Converting between kilograms and stones is something millions of people in the United Kingdom do every day — whether stepping off the bathroom scales, visiting the GP, or monitoring weight-loss progress. Despite the UK adopting the metric system for most purposes, the stone remains deeply embedded in British culture as the preferred unit for expressing personal body weight. This guide covers everything you need to know about the kg to stones conversion, including the exact formula, a complete reference table, and BMI context so you can understand what your weight means for your health.
The Exact kg to Stones Formula
The conversion is straightforward once you know the key relationship: 1 stone = 6.35029 kilograms. This is the official definition under the UK Weights and Measures Act. To convert kilograms to stones, divide your kilogram value by 6.35029. To get stones and pounds separately, take the decimal portion of the result and multiply it by 14 (since there are 14 pounds in a stone).
Formula: Stones = kg ÷ 6.35029
Example: 80kg ÷ 6.35029 = 12.598 stones. The whole number is 12 stone. The remainder 0.598 × 14 = 8.37 pounds. So 80kg = 12 stone 8.4 pounds.
Going the other way, to convert stones to kilograms, simply multiply by 6.35029. And to convert pounds to kilograms, multiply by 0.453592 (since 1 pound = 0.453592 kg).
Why the UK Uses Stones for Body Weight
The stone is one of Britain's oldest units of measurement. It was used across medieval Europe but became standardised in England at 14 pounds by the Weights and Measures Act of 1824. When the UK officially adopted the metric system in the 1970s and 1980s, most trade measurements switched to metric units — but the stone was never legally abolished for personal weight. The result is a uniquely British hybrid: your GP will measure you in kilograms, your bathroom scales might display both, and yet most British people naturally think and talk about their weight in stones and pounds.
This cultural persistence is remarkable. A 2023 survey found that over 70% of UK adults still primarily think of their body weight in stones and pounds rather than kilograms, even among younger generations. The NHS, while using kg for clinical purposes, displays BMI charts with stone equivalents for patient understanding.
Understanding BMI in Stones and Kilograms
Body Mass Index (BMI) is calculated using kilograms and metres: BMI = weight (kg) ÷ height (m)². The NHS defines the following BMI categories:
- Underweight: Below 18.5
- Healthy weight: 18.5 to 24.9
- Overweight: 25 to 29.9
- Obese: 30 and above
For a person who is 5 feet 8 inches tall (172.7cm), the healthy weight range is approximately 55.3kg to 74.5kg (8 stone 10lb to 11 stone 10lb). For someone who is 5 feet 10 inches tall (177.8cm), the healthy range is 58.5kg to 79kg (9 stone 3lb to 12 stone 6lb). Our calculator above shows your BMI category whenever you enter a height alongside your weight.
BMI is a useful screening tool but has limitations — it does not account for muscle mass, age, ethnicity, or fat distribution. Athletes may have a high BMI despite being very healthy, while older adults may have a normal BMI but carry too much visceral fat. Always discuss your weight with an NHS healthcare professional for personalised advice.
Common Stone and Kilogram Equivalents
Here are the most frequently looked-up weight conversions in the UK:
- 8 stone = 50.8 kg | 8 stone 7 lb = 53.98 kg
- 9 stone = 57.15 kg | 9 stone 7 lb = 60.33 kg
- 10 stone = 63.5 kg | 10 stone 7 lb = 66.68 kg
- 11 stone = 69.85 kg | 11 stone 7 lb = 73.03 kg
- 12 stone = 76.2 kg | 12 stone 7 lb = 79.38 kg
- 13 stone = 82.55 kg | 13 stone 7 lb = 85.73 kg
- 14 stone = 88.9 kg | 14 stone 7 lb = 92.08 kg
- 15 stone = 95.25 kg | 16 stone = 101.6 kg
- 17 stone = 107.95 kg | 18 stone = 114.3 kg
- 20 stone = 127 kg | 25 stone = 158.76 kg
Kilograms to Stones and Pounds — Full Conversion Table (40kg–150kg)
The table below covers the full range from 40kg to 150kg in 1kg steps, showing stones, pounds, and total pounds for quick reference.
| kg | Stones | st & lb | Total lbs |
|---|
Kilograms to Stones in Everyday Life
Understanding weight conversions is useful in many UK contexts beyond personal health. When buying or selling second-hand goods, items like gym equipment, luggage, and produce may be listed in either kilograms or pounds. UK airlines and travel companies express luggage allowances in kilograms, while older luggage scales may show stones and pounds. Most modern bathroom scales in the UK display in both units or allow you to toggle between them.
In the medical context, prescription medications that are dosed by body weight (such as chemotherapy drugs, warfarin, and some antibiotics) always use kilograms. This makes it essential that UK patients know their weight in kg as well as stones. Children's medication doses are almost always calculated in kilograms per kilogram of body weight (mg/kg), so knowing your child's weight in kilograms is important for safe medication administration.
For sports and fitness, boxing weight classes use pounds as the official measure, while many UK gyms display weight equipment in kilograms. Powerlifting and weightlifting competitions in the UK use kilograms for both body weight categories and lift totals. Understanding both systems makes it easier to follow sporting events and compare performances across different records.
Comparing with US and Other Measurement Systems
Unlike the UK, the United States does not use stones at all — Americans express body weight exclusively in pounds. So while a British person might say they weigh "12 stone 4", their American counterpart would say "172 pounds" (the equivalent). Australians and Canadians have fully metricated and use kilograms exclusively. This makes the stone uniquely British and Irish — the Republic of Ireland also retains the stone for informal personal weight discussions, despite being fully metric for official purposes.
Weight Loss Tracking in Stones
For weight loss purposes, tracking progress in stones can feel more motivating for many UK people, as reaching a new "stone milestone" (e.g., dropping from 13 stone to 12 stone) provides a clear psychological reward. In kilogram terms, this represents crossing each 6.35kg threshold. If you are working with a NHS weight management programme or a slimming group like Slimming World or Weight Watchers UK, conversions between kilograms and stones are needed frequently. Our calculator above handles all these conversions instantly and bidirectionally.