Convert Weight from Stones to Kilograms (st to kg)

Stone to Kilogram Conversion Formula

Example

Let's convert 5 Stone (st) to Kilogram (kg).

Using the formula:

Therefore, 5 Stone (st) is equal to 31.7514659 Kilogram (kg).

How many stones are in one kilogram? One Kilogram (kg) contains 0.15747304441776970052 Stones (st) — the inverse of the factor above. Multiplying by 6.35029318 takes you from stones to kilograms; multiplying by 0.15747304441776970052 brings you back.

Put in words: one stone equals 6.35029318 kilograms, so the stone is the larger unit of this pair. Converting between them never changes the amount of weight being measured — only the size of the unit you count it in.

What is a Stone (st)?

The stone (st) is a unit of measurement equal to 14 pounds (lb).

It's part of the imperial system and is still commonly used in a few countries, especially for weighing people.

How Many Kilograms are in a Stone?

For use in international contexts or scientific applications, the stone is often converted to the metric system.

One stone is equal to exactly 6.35029318 kilograms (kg).

This precise conversion is used in international trade and science to ensure everyone is using the exact standard measurement.

Why is Body Weight Measured in Stone?

Although it's an older unit, the stone remains the primary unit of measurement for body weight in the United Kingdom and Ireland.

It's common to hear someone state their weight as a combination of stone and pounds, like "12 stone 6 pounds."

Where Did the Stone Unit Come From?

The stone traces its origins back to the medieval English wool trade, where a "stone of wool" referred to a standard 14-pound measure used for buying and selling.

Stones for other goods could vary in weight—for example, a stone of glass was just 5 pounds—but over time, the 14-pound stone became the official legal standard.

How the Stone Is Actually Written

The stone is almost never used on its own. Body weight in Britain and Ireland is quoted as stones and pounds, with the remainder written out rather than expressed as a decimal.

A person weighing 72 kg is "11 stone 4" — that is 11 st 4 lb, or 158 pounds — not "11.3 stone". Reading the decimal form as pounds is a common error: 11.3 st is 11 st 4.2 lb, close by coincidence, but 11.5 st means 11 st 7 lb, not 11 st 5 lb.

The conversions worth keeping to hand are:

• 1 stone = 14 pounds = 6.35029 kilograms
• 1 kilogram ≈ 0.157473 stone
• A useful mental check: 10 stone ≈ 63.5 kg, and each additional stone adds a little over 6 kg.

Where the Stone Is and Is Not Used

The unit's survival is unusually specific. It was removed from British trade use by weights and measures legislation, so nothing is sold by the stone — shop scales read in kilograms and grams.

What survives is personal and conversational use: body weight, and by extension the weight of livestock and sporting figures such as boxing and horse-racing weights. Medical records in the UK are kept in kilograms, but patients are routinely told their weight in stones and pounds because that is the number they recognise.

Outside Britain and Ireland the unit is essentially unknown. The United States, despite sharing the pound, does not use the stone at all — American body weight is quoted in pounds alone, which is why a US figure of "158 lb" and a UK figure of "11 st 4" describe exactly the same person.

What is a Kilogram (kg)?

A kilogram (kg) is the base unit of mass in the metric system, used worldwide to measure everything from your body weight to the groceries you buy.

It's equal to 1,000 grams (g).

For a simple real-world comparison, the mass of a one-liter bottle of water is almost exactly one kilogram.

Key Takeaways

• A kilogram is 1,000 grams.
• The kilogram is now defined by the Planck constant, a fundamental constant of nature.
• Previously, it was defined by a physical metal cylinder in France named "Le Grand K."
• It is the only SI base unit that has a prefix ("kilo") in its name.

How Is the Kilogram Defined Today? From an Object to a Constant

For more than 130 years, the kilogram was a physical object: a platinum-iridium cylinder called the International Prototype Kilogram (IPK), also known as "Le Grand K," which was kept under tight security near Paris.

Scientists eventually found the problem — the artifact was losing an imperceptible amount of mass over time — so it couldn't guarantee the long-term accuracy required by science and industry.

On May 20, 2019, the kilogram was redefined.

It's no longer tied to a single object but to a fundamental constant of nature: the Planck constant (h). That change makes the kilogram stable and reproducible with precision anywhere in the universe.

What Was the Original Definition of the Kilogram?

The kilogram's story begins during the French Revolution with the creation of the metric system. The original definition, established in 1795, was beautifully simple and practical.

The gram was first defined as the mass of one cubic centimeter of water at 4 °C (39.2 °F), the temperature at which it is most dense.

From there, the kilogram was defined as the mass of one liter (one cubic decimeter) of water under the same conditions. This practical, water-based definition was a revolutionary step toward a global standard of measurement.

Why Is the Kilogram a Unique SI Base Unit?

The International System of Units (SI) is built on seven base units that serve as the foundation for all measurements. These include the meter for length, the second for time, and the ampere for electric current.

The kilogram is a historical oddity, as it's the only SI base unit with a prefix ("kilo").

Due to its origins, the kilogram, rather than the gram, became the fundamental unit of mass, making it a curious exception in the measurement system.

Stone to Kilogram Conversion Table

Here are some quick reference conversions from Stone (st) to Kilogram (kg):