Stones to Kilograms Converter

The stones to kilograms converter is a fast, free, two-way weight calculator that switches between UK / Ireland stones (st) and metric kilograms (kg) in a single step. Type a value in either field and the other updates instantly. The result also shows pounds (lb), broken into the canonical UK whole-stone plus residual-pounds form ("11 st 4 lb"), because stones are almost never written alone in British and Irish everyday usage. The math is anchored to the UK Weights and Measures Act 1985, which defines the stone as exactly 14 international avoirdupois pounds, and the 1959 international yard and pound agreement, which defines the pound as exactly 0.45359237 kilograms. Combining the two, one stone equals 6.35029318 kilograms exactly.

Because the stone is defined as 14 pounds and the pound is defined as 0.45359237 kilograms, both by statute rather than measurement, the conversion carries no experimental uncertainty. The displayed inverse factor 0.1574730444 stones per kilogram is the rounded reciprocal of 6.35029318. To four decimal places, every result this converter produces is accurate to better than one gram, which is far more than the precision of any consumer bathroom scale.

How to Use the Stones to Kilograms Converter

1. Type a value in the Stones (st) field. The default is 1 st, which equals 6.3503 kg.
2. Watch the Kilograms (kg) field update instantly as you type, using the exact factor 6.35029318 kg per stone.
3. Or type a value in the kilograms field. The stones field updates instantly using the inverse factor 0.1574730444 st per kg.
4. Read the combined result line below the inputs. It reads as "X stone Y lb = Z kg = W lb", where X is a whole number of stones, Y is the residual pounds (0 to 13), Z is the kilogram value to four decimal places, and W is the total pounds to the nearest whole pound.
5. Press the ⇄ Swap button to flip the units without retyping the value, or Copy result to put the combined line on your clipboard for a medical form, BMI calculator, or chat message.

the Stones To Kg runs entirely in your browser. Inputs never leave your device. There is no rate limit, no sign-up, no advertising, and no data collection.

The Formulas

Stones to kilograms, multiply the stone value by the exact factor 6.35029318:

kilograms = stones × 6.35029318

This factor is the product of two exact international definitions: 1 stone = 14 lb (UK Weights and Measures Act 1985) and 1 lb = 0.45359237 kg (1959 international yard and pound agreement). For a 10 stone adult, the math is 10 × 6.35029318 = 63.5029 kg. For an 11 st 4 lb adult, the math is (11 × 14 + 4) × 0.45359237 = 158 × 0.45359237 = 71.6676 kg.

Kilograms to stones, divide the kilogram value by 6.35029318:

stones = kilograms ÷ 6.35029318

For a 70 kg adult, the math is 70 ÷ 6.35029318 = 11.0231 st. The decimal result is conventionally read as a whole number of stones plus a residual 0 to 13 pounds, for example, 11.0231 st reads as "11 st 0 lb".

Quick mental shortcut, 1 stone is approximately 6.35 kg, and 1 kg is approximately 0.1575 stone. So a 12 st person is roughly 76 kg, and a 76 kg person is roughly 12 st. These approximations are accurate to about 0.05%, which is enough for everyday conversation but not for medical dosing or BMI precision.

Worked Examples

Example 1, Convert 1 stone to kilograms (a basic sanity check).

1. Apply the factor: kilograms = 1 × 6.35029318.
2. Compute: 1 × 6.35029318 = 6.35029318.
3. Round to four decimal places: 6.3503 kg.

1 stone is exactly 6.3503 kg to four decimal places, and the equivalent is 14 lb.

Example 2, Convert 10 stone to kilograms (a typical UK adult body weight).

10 × 6.35029318 = 63.5029 kg (also 140 lb). A 10 st adult sits in the middle of the UK body-weight distribution; the Office for National Statistics reports a mean adult weight of about 70.2 kg (11 st 1 lb) for men in England.

Example 3, Convert 11.5 stone to kilograms (a half-stone reading).

11.5 × 6.35029318 = 73.0284 kg (also 161 lb). Half-stone readings are common on British bathroom scales, which usually step in 0.2-stone increments but read to half a stone in display.

Example 4, Convert 73 kg to stones and pounds.

73 ÷ 6.35029318 = 11.4961 st, which splits as 11 st and a residual 0.4961 st. The residual converts to pounds: 0.4961 × 14 = 6.95 lb, rounded to 7 lb. Result: 11 st 7 lb, which is 73.0284 kg back the other way. The residual is always clamped to 0 to 13 lb so the breakdown stays canonical.

Example 5, Convert 12 stone 8 pounds to kilograms (a stone-and-pounds reading).

1. Add the pounds first to get total pounds: 12 × 14 + 8 = 176 lb.
2. Convert pounds to kilograms: 176 × 0.45359237 = 79.8323 kg.

A 12 st 8 lb adult weighs 79.8323 kg, or 176 lb total, the input style used by NHS BMI calculators, gym sign-in sheets, and British medical charts. 8 stone equals 50.8023 kg (112 lb), a typical reading for a smaller-framed adult.

Where It Shows Up

• Body weight in the UK and Ireland. Bathroom scales sold in Britain typically have a "st/lb" mode, and medical and fitness apps in those countries report body weight in stone and pounds by default. This converter bridges to kilograms for international readers, BMI calculators, metric drug-dosing charts, and luggage limits.
• NHS BMI calculator. The UK NHS online BMI calculator accepts either metric (kg) or imperial (stones and pounds) input. To use it with an imperial reading from a UK scale, convert to kilograms here first.
• Luggage and travel. Most international airlines apply a 23 kg checked-bag limit. UK travellers who weigh themselves in stones need the kilogram equivalent before they pack; a typical 12 st adult plus a suitcase often exceeds the 23 kg limit by a noticeable margin.
• Sports and athletic performance. Boxing weight classes, horse racing handicaps, and rowing crew weights in the UK and Ireland are still published in stones and pounds; international audiences see the same numbers in kilograms.
• Recipe and grocery conversion. Butchers, greengrocers, and farm-shop price lists often quote weight in pounds or stone and pounds. A joint of beef at "3 lb" is 1.36 kg.
• Health statistics and surveys. The Office for National Statistics and NHS Digital health surveys report body weight in kilograms in their published tables but routinely use stones and pounds in their press releases and infographics.

Common Mistakes

• Confusing UK stones with the US informal "stone". The US informally uses "stone" for 14 lb in some weight-loss contexts, but British body weight is the canonical case. A US doctor will rarely write "12 stone" on a chart, they will write "168 lb". The number is the same: 12 st = 168 lb = 76.2035 kg.
• Ignoring the 14 lb per stone convention. Some sources quote body weight as if 1 st = 6 kg or 1 st = 7 kg. The exact international figure is 6.35029318 kg. The 6 kg approximation understates by 5.5%; the 7 kg approximation overstates by 10.2%. Neither is acceptable for medical use.
• Mixing troy and avoirdupois pounds. The stone uses the avoirdupois pound (0.45359237 kg). The troy pound (0.373242 kg) is used for precious metals and is unrelated.
• Rounding stones to the nearest whole number too early. Converting 73 kg to stones gives 11.4961 st, which is canonical "11 st 7 lb" (rounded). Writing just "11 st" loses 7 lb (3.18 kg) of information; writing "11.5 st" loses 7 lb (3.18 kg) in the other direction.
• Using a kilogram-to-pound converter and ignoring stones. A 12 st adult reads as "168 lb" or "76.2 kg". Going through the stones step is only worth it when the source or destination uses stones.
• Adding stones and pounds before converting. 11 stone plus 4 pounds is not 15 stone or 15.4 stone, it is 11 + 4/14 = 11.2857 stone, which is 71.6676 kg. Convert both parts to kilograms separately and add, or convert pounds to a decimal stone first.

Frequently Asked Questions

How many kilograms are in a stone?

One stone is exactly 6.35029318 kilograms. The factor is the product of two exact international definitions: 1 stone = 14 lb (UK Weights and Measures Act 1985) and 1 lb = 0.45359237 kg (1959 international yard and pound agreement). To convert stones to kilograms, multiply by 6.35029318 and round to the desired precision.

How many stones are in a kilogram?

One kilogram is exactly 0.1574730444 stones (to ten decimal places), which is the rounded reciprocal of 6.35029318. To convert kilograms to stones, divide by 6.35029318. For body-weight purposes the result is conventionally read as a whole number of stones plus a residual 0 to 13 pounds, for example, 73 kg = 11.4961 st ≈ 11 st 7 lb.

Is 1 stone equal to 6.35 kg or 6.35029318 kg?

Both are correct, with different precision. 1 stone = 6.35029318 kg exactly, since both the stone and the pound are defined by statute. The 6.35 figure is accurate to four significant figures and is the form most quick-reference tables use; it is rounded down by about 0.004% relative to the exact value. For medical, pharmaceutical, or freight use, keep all eight digits.

How do I convert 11 stone 4 pounds to kilograms?

Add the pounds first to get the total: 11 × 14 + 4 = 158 lb. Then multiply by 0.45359237 kg per pound: 158 × 0.45359237 = 71.6676 kg, which rounds to 71.668 kg. This converter does both steps automatically, type 11 in the stones field and read the kilograms result with the residual pounds split out as "11 st 4 lb".

Why does the UK use stones for body weight?

The stone was the standard unit for trade in medieval England and was formalised in English law by the 14th century, when the 14-pound stone became the convention for weighing wool and other bulk goods. It persisted for personal body weight long after metrication of other measures because everyday speech never replaced it. Ireland adopted the stone during British rule and is the only other country that still uses it in everyday speech.

How accurate is the stone-to-kilogram conversion?

The conversion is exact. Both the stone (as 14 lb) and the pound (as 0.45359237 kg) are defined by statute, so the resulting kilogram value carries no measurement uncertainty. The only source of error in a displayed value is how many decimal places are kept when rounding for display. To four decimal places, the converter is accurate to about 0.1 g, which is far more than the precision of any consumer bathroom scale.

What is the difference between a stone and a kilogram?

A stone is a UK / Ireland traditional unit of mass equal to exactly 14 international avoirdupois pounds or exactly 6.35029318 kilograms. A kilogram is the SI base unit of mass, defined since 2019 by a fixed value of the Planck constant. The stone is a derived unit in the imperial system; the kilogram is the foundational unit in the metric system.

Do other countries use the stone?

Only the UK and Ireland use the stone in everyday speech. Some Commonwealth countries, Canada, Australia, New Zealand, historically used the stone for body weight and switched to kilograms alongside general metrication in the 1970s and 1980s. The US never adopted the stone; body weight there is in pounds only. Continental European countries use kilograms.

How do I convert stones to pounds?

Multiply the whole-stone figure by 14 and add the residual pounds. 11 st 4 lb = 11 × 14 + 4 = 158 lb. Going from kilograms to pounds directly, multiply by 2.2046226218 (the reciprocal of 0.45359237). 73 kg × 2.2046226218 = 160.94 lb. The converter exposes both intermediate steps in the result line.

What is the BMI for 11 stone?

BMI depends on height, since BMI = weight (kg) ÷ height (m)². 11 stone = 69.853 kg. For a 1.75 m adult, BMI = 69.853 / 3.0625 = 22.8 (normal range). For a 1.65 m adult, BMI = 69.853 / 2.7225 = 25.7 (overweight range). Use a BMI calculator with your height for a personalised reading.

Is 12 stone overweight?

Not necessarily. Whether 12 stone (76.2 kg) is overweight depends on height, muscle mass, and body composition. For a 1.80 m adult, BMI = 76.2 / 3.24 = 23.5, in the normal range (18.5 to 24.9). For a 1.60 m adult, BMI = 76.2 / 2.56 = 29.8, in the overweight range. Use a BMI calculator with your height for a personalised reading.

Why does the converter show pounds alongside kilograms?

UK and Ireland body-weight readings are almost always quoted as a whole number of stones plus a residual pounds value (e.g. "11 stone 4 lb"). Showing only kilograms hides that convention; showing kilograms plus the stone / pound breakdown lets the result be read in either British form or metric form without losing precision. The converter keeps kilograms as the SI anchor and derives the breakdown from it.

References

• Weights and Measures Act 1985 (UK). The UK statute that defines the stone as exactly 14 pounds, the pound as exactly 0.45359237 kilograms, and the yard as exactly 0.9144 metres. The Act adopts the international yard and pound agreement of 1959 for use in the United Kingdom.
• International Yard and Pound Agreement, 1959. Signed by the United States, the United Kingdom, Canada, Australia, New Zealand, and South Africa. Fixed the yard at exactly 0.9144 metres and the pound at exactly 0.45359237 kilograms. The agreement resolved small (~0.0002%) differences between the historical US and UK pounds.
• Bureau International des Poids et Mesures (BIPM). The SI Brochure (9th edition) defines the kilogram since 2019 by a fixed value of the Planck constant (h = 6.62607015 × 10⁻³⁴ J⋅s) and documents the relationship between the kilogram and the international avoirdupois pound.
• National Institute of Standards and Technology (NIST). NIST Special Publication 811 (Guide for the Use of the SI Units) reproduces the 1959 yard and pound agreement values and is the authoritative US reference for kg ↔ lb conversions.
• Office for National Statistics (UK). Adult body-weight distribution statistics published by the ONS, including the mean body weight for adults in England, are reported in kilograms but routinely converted to stones and pounds for press releases.
• NHS BMI calculator. The UK National Health Service online BMI calculator accepts either metric (kg) or imperial (stones and pounds) input. The metric and imperial inputs give the same BMI reading, with the conversion done internally.

Related Tools

• Kilograms to Pounds Converter, convert between metric kilograms and imperial pounds in a single step. Useful when stones are not part of the source or destination.
• Stone to Kilograms Converter, sibling tool with the same conversion factors and a slightly different layout, focused on UK / Ireland body weight presets from 8 to 18 stone.
• Mass / Weight Converter, convert any mass between metric and imperial units including kilograms, grams, pounds, ounces, stones, and metric tons.
• BMI Calculator, calculate Body Mass Index from weight and height in either metric or imperial units. Accepts a stones-and-pounds input.
• Pounds to Kilograms Converter, convert pounds to kilograms and kilograms to pounds instantly, using the exact factor 1 lb = 0.45359237 kg.