Stone ⇄ Kilograms

Stone and Kilograms: Complete Guide to Conversion, Formula, Body Weight Charts, and Practical Applications

The stone is a traditional unit of weight still widely used in the United Kingdom and Ireland for expressing body weight. While the rest of the world uses kilograms and the United States uses pounds, millions of people in the UK and Ireland think of their weight in stone. Whether you are interpreting medical records, tracking fitness goals, comparing weight across different systems, or simply curious about your weight in another unit, this bidirectional converter provides instant, accurate results with a comprehensive breakdown.

The Conversion Factor

One stone equals exactly 6.35029318 kilograms (commonly rounded to 6.35029 kg). This derives from the definition that 1 stone = 14 avoirdupois pounds, and 1 pound = 0.45359237 kg exactly. Therefore 14 × 0.45359237 = 6.35029318 kg. To convert stone to kg, multiply by 6.35029. To convert kg to stone, divide by 6.35029. The result in stone is often expressed as "X stone Y pounds" — for example, 75 kg = 11 stone 11.5 lbs.

Stone and Pounds Notation

In the UK and Ireland, body weight is typically expressed as "X stone Y pounds" rather than decimal stone. For instance, someone weighing 76 kg would say "11 stone 13 pounds" (often written "11 st 13 lbs" or simply "11.13" in casual notation — though this is ambiguous). To convert decimal stone to stone-and-pounds: take the whole number as stone, multiply the decimal remainder by 14 to get pounds. For example, 11.929 stone: 11 stone and 0.929 × 14 = 13.0 lbs = "11 stone 13 lbs." This converter automatically shows the stone-and-pounds breakdown for every result.

Common Body Weight Conversions

Here are the most frequently searched body weight conversions between stone and kilograms: 8 stone = 50.8 kg (112 lbs), 9 stone = 57.2 kg (126 lbs), 10 stone = 63.5 kg (140 lbs), 11 stone = 69.9 kg (154 lbs), 12 stone = 76.2 kg (168 lbs), 13 stone = 82.6 kg (182 lbs), 14 stone = 88.9 kg (196 lbs), 15 stone = 95.3 kg (210 lbs). Going the other direction: 60 kg = 9 st 6 lbs, 70 kg = 11 st 0 lbs, 80 kg = 12 st 8 lbs, 90 kg = 14 st 2 lbs, 100 kg = 15 st 10 lbs.

Medical and Health Context

UK medical records traditionally used stone for patient weight, though the NHS has been transitioning to kilograms. Medication dosing, BMI calculations, and clinical guidelines use kilograms exclusively. A patient might tell their GP they weigh "12 stone" but the prescription system needs 76.2 kg. BMI is calculated as weight in kg divided by height in meters squared — so stone must be converted to kg first. This converter makes that translation instant. Understanding both systems helps patients communicate effectively with healthcare providers and interpret medical information correctly.

Fitness and Weight Management

People tracking weight loss or muscle gain in the UK often set goals in stone ("I want to get below 11 stone") while gym equipment, fitness apps, and international programs display kilograms. A common weight loss goal of "losing a stone" means losing 6.35 kg or 14 lbs. Gym weight plates in the UK are typically in kilograms (2.5 kg, 5 kg, 10 kg, 20 kg), so understanding the conversion helps when following lifting programs expressed in stone or pounds. A 100 kg bench press is 15 stone 10 lbs — or equivalently, 220.5 lbs.

History of the Stone

The stone has been used in the British Isles for over a thousand years. Originally it varied by commodity — a stone of wool weighed 14 lbs, but a stone of butcher's meat was 8 lbs, and a stone of cheese was 16 lbs. The 14-pound stone was standardized by royal decree and became the sole legal definition by 1835. While the UK officially adopted the metric system in 1985, the stone remains deeply embedded in British and Irish culture for expressing body weight — much like the US retained the pound. It is rarely used in professional or scientific contexts but remains ubiquitous in casual conversation, media, and everyday life.

Boxing and Combat Sports

Boxing weight classes in the UK are often discussed in stone. Welterweight (up to 147 lbs = 10 st 7 lbs = 66.7 kg), middleweight (up to 160 lbs = 11 st 6 lbs = 72.6 kg), and heavyweight (over 200 lbs = 14 st 4 lbs = 90.7 kg) are common reference points. Fighters cutting weight might say they need to "make 10 stone" meaning they need to weigh in at or below 63.5 kg. International boxing uses kilograms for official weigh-ins, so conversion is essential for following the sport across UK and international media.

How to Use This Converter

This is a bidirectional converter — type in either the stone or kilograms field and the other updates automatically. Quick-value buttons provide common body weights for both units. The swap button exchanges the two values. Press "Convert" to see the full breakdown: all weight units, stone-and-pounds notation, step-by-step calculation, body weight reference chart, and contextual insight. The reference chart covers the full adult body weight range from 6 to 25 stone.