Stone, Pounds and Kilograms Explained

What a stone is

The stone is a unit of mass equal to 14 avoirdupois pounds. Its abbreviation is st. Since the pound is defined as exactly 0.45359237 kg, one stone is exactly 14 × 0.45359237 = 6.35029318 kg, or about 6.35 kg.

Plural usage can look odd: people say “ten stone” rather than “ten stones”, and often give a weight as stone and pounds together, such as 11 stone 4, meaning 11 stone and 4 pounds. That mixed style is the main reason the unit causes confusion for people used to a single number.

Where the stone is still used

The stone remains common for personal body weight in the United Kingdom and Ireland. It also appears in some sports, including boxing and horse racing. It is not a normal everyday unit in the United States, where body weight is given in pounds, and it is not used in countries that rely on kilograms.

Its status in trade is different from its place in conversation. The UK Weights and Measures Act 1985 removed the stone from the units permitted for trade, and Ireland passed similar legislation in 1983. In practice that means official and commercial weighing uses kilograms or pounds, while the stone lives on mainly in speech, in personal health conversations and in some sporting contexts.

Stone and pounds to kilograms

The method has two steps. First, turn the stone into pounds by multiplying by 14 and adding any extra pounds. Second, multiply the total pounds by 0.45359237.

For 11 stone 4 pounds, 11 × 14 = 154 and 154 + 4 = 158 lb. Then 158 × 0.45359237 = 71.66759446 kg, which rounds to 71.7 kg. For a round figure, 10 stone is 140 lb, which is 63.5029318 kg, or about 63.5 kg. A second example: 9 stone 7 pounds is 9 × 14 + 7 = 133 lb, and 133 × 0.45359237 = 60.33 kg. If the result looks unreasonable, recheck the first step, because forgetting to add the extra pounds, or multiplying by 12 instead of 14, are the most frequent slips.

You can also go straight from stone to kilograms by multiplying by 6.35029318. Doing the pounds separately is easier to check by hand, though, because multiplying by 14 is quick to do mentally.

Kilograms to stone and pounds

Starting from kilograms, first find pounds by multiplying by 2.2046226, then split the total into stone and a remainder. Divide by 14 and keep the whole number as stone; the leftover is pounds.

Take 65 kg. Then 65 × 2.2046226 = 143.30 lb. Fourteen goes into 143.30 ten times, since 10 × 14 = 140, leaving 3.30 lb. So 65 kg is 10 stone 3.3 lb. Another example is 80 kg: 80 × 2.2046226 = 176.37 lb, and 12 × 14 = 168, which leaves 8.37 lb, so 80 kg is 12 stone 8.4 lb.

The remainder is often rounded to the nearest half pound or whole pound, because bathroom scales are rarely more precise than that.

Decimal stone and how to read it

A converter that gives a single number will show stone as a decimal. Dividing 65 kg by 6.35029318 gives 10.2357 stone. The decimal part is not pounds. To get the pounds, multiply the part after the decimal point by 14: 0.2357 × 14 = 3.30 lb. That agrees with the result above.

A common error is reading 10.2 stone as 10 stone 2 pounds. It is actually 10 stone and 0.2 × 14 = 2.8 pounds. The difference is under a pound here, but with a value like 10.5 stone the gap is large: that is 10 stone 7 pounds, not 10 stone 5.

Quick estimates

For a rough conversion, treat one stone as 6.35 kg, or just over 6 kg. Ten stone is then about 63.5 kg. Going the other way, doubling a weight in kilograms and adding a tenth gives pounds, and dividing the pounds by 14 gives stone. Each estimate lands within a pound or two, which is close enough to sense-check a calculator result.

These reference values follow directly from the exact factor and are rounded to one decimal.

• 8 stone = 112 lb = 50.8 kg
• 10 stone = 140 lb = 63.5 kg
• 12 stone = 168 lb = 76.2 kg
• 14 stone = 196 lb = 88.9 kg

Using a converter and checking the source

A unit converter such as this one includes stone, pound and kilogram in its Mass category, and shows the same mass in every unit at once, so you can read the stone figure and the pound figure side by side. You can set the number of decimal places, and a comma works as a decimal separator.

It converts a single number, so enter the total in pounds or the decimal in stone and split it yourself as shown above. For health records, clinical decisions or anything with legal weight, use the figures given by the original source and keep its units. If a record gives stone and pounds, write down both parts before converting, so that the pounds are not lost along the way.