What is a Stone? — History & Definition
The stone (st) is a British imperial unit of weight equal to exactly 14 pounds, or 6.35029 kg. Still widely used today across the UK for measuring body weight.
Where Did the Stone Come From?
Historically, trading communities evaluated agricultural goods using physical native stones. Because a physical rock could vary widely depending on the region, the official weight of a "stone" shifted enormously across European countries ranging anywhere from 3 kg to over 15 kg depending on the city.
It wasn't until the Weights and Measures Act of 1835 that the British Crown formally standardized the stone for trade to exactly 14 pounds (lbs).
Countries That Still Use It
Today, the stone is almost exclusively used formally and informally in the United Kingdom and Ireland. While the UK legally adopted the metric system and officially measures medical weight in kilograms, civilian culture continues to instinctively express human body mass in stones and pounds.
The United States, having split off before the 1835 standardization, relies almost entirely on pounds and overlooks the stone entirely in modern vocabulary.
Stone vs Kilogram
- 1 Stone = 6.35029 kg
- 1 Kilogram = 0.15747 st
- 1 Stone = 14 Pounds
A Brief Timeline
Pre-1300s
Physical stones used as weights in local European markets. Values varied widely by region — from 3 kg to over 15 kg.
1350
England standardizes the wool stone at 14 pounds. Wool was the primary trade commodity and drove the need for consistency.
1835
The Weights and Measures Act formally standardizes the stone to exactly 14 pounds across all British trade and commerce.
1985
UK legislation requires metric units for official trade. However, the stone remains culturally dominant for human body weight.
Today
The stone is used informally across the UK and Ireland for body weight. Doctors record weight in kilograms — hence why you need to convert.
Why This Still Matters Today
The stone is embedded in everyday UK life. You will encounter it on weighing scales, in casual health conversations, and in pharmacies. But official medical settings — GP surgeries, hospitals, prescriptions — all use kilograms. Knowing how to convert between the two is a genuinely practical skill.
GP Appointments
Doctors and nurses record weight in kg. If your scale shows stone, you need to convert before your appointment.
Fitness & Nutrition Apps
Most international apps use kg. Converting your starting weight correctly ensures accurate tracking.
Online Health Calculators
BMI tools, calorie calculators, and medication dosage guides all use kilograms as the standard input.
Frequently Asked Questions
What is a stone?
A stone is a unit of weight in the imperial system equal to exactly 14 pounds or 6.35029 kilograms.
Who still uses the stone measurement?
The stone is primarily used in the United Kingdom and Ireland today for informally expressing human body weight.
Why doesn't America use the stone?
The US customary system adopted the pound (lb) as the primary weight unit before the stone became formally standardized for trade in Britain in 1835.