Why does the UK measure body weight in stone?

The stone as a weight unit originated in medieval England's wool trade. Merchants used actual stones as counterweights on balance scales. In 1350, Edward III standardized the wool stone at 14 pounds to create consistency across trading markets. The unit became so embedded in daily life that it survived metrication — the UK officially adopted metric in 1965 but stone persists culturally for body weight.

How many pounds in a stone?

One stone equals exactly 14 pounds. This relationship is fixed and has been the legal definition since the Weights and Measures Act 1824 in the UK. To convert stone to pounds, multiply by 14. To convert pounds to stone, divide by 14.

What is 12 stone in kg?

12 stone equals 168 pounds, which equals 76.2 kg exactly. The formula is: kg = stone × 6.35029. One stone = 6.35029318 kg (exactly, since 1 kg = 2.20462 lbs and 1 stone = 14 lbs). So 12 × 6.35029 = 76.20 kg.

Why Does the UK Use Stone for Weight? History & Conversion Guide

The Medieval Origins of the Stone

Before standardized weights, merchants literally used smooth river stones as counterweights on balance scales. Different trades used different-sized stones: a "wool stone" was not the same weight as a "butcher's stone" or a "cheese stone." By the 14th century, this inconsistency was causing commercial chaos across England's vital wool export trade.

In 1350, King Edward III issued a statute fixing the wool stone at 14 pounds. This standardization helped English wool merchants trade consistently with Flemish buyers in Bruges and Ghent — the biggest textile market in Europe at the time. The 14-pound stone became so ingrained in English commerce that no subsequent reform could dislodge it.

Stone to Pounds and Kilograms Conversion Table

One stone = 14 pounds = 6.35029 kg (exact by definition).

Stone	Pounds	Kilograms	BMI Category (approx., 5'7" / 170 cm)
8 st	112 lb	50.8 kg	Underweight
9 st	126 lb	57.2 kg	Healthy weight
10 st	140 lb	63.5 kg	Healthy weight
11 st	154 lb	69.9 kg	Healthy weight
12 st	168 lb	76.2 kg	Overweight
13 st	182 lb	82.6 kg	Overweight
14 st	196 lb	88.9 kg	Obese Class I
15 st	210 lb	95.3 kg	Obese Class I
16 st	224 lb	101.6 kg	Obese Class II
18 st	252 lb	114.3 kg	Obese Class II
20 st	280 lb	127.0 kg	Obese Class III

Why Doesn't the US Use Stone?

The United States broke with British measurement conventions early in its history. American merchants and physicians adopted the pound as the primary weight unit for body mass, partly because the young republic wanted commercial independence and partly because the pound was already the dominant unit in colonial trade records. When the metric system was later debated in the US (1860s–1970s), no conversion happened for everyday use, leaving Americans with pounds rather than stone or kilograms.

Where Stone Is Still Used Today

Stone remains in common use for body weight in the United Kingdom, Ireland, and some Commonwealth countries. It does not appear on product packaging (which must show kg by EU/UK law) or in scientific contexts. British doctors record official medical weights in kilograms, but patients routinely report their weight in stone. Gym scales in the UK often display all three: stone, pounds, and kilograms.

Convert stone, pounds, and kilograms with our weight converter.