Kilograms to Stones Converter

The kilogram (kg) is the SI base unit of mass used worldwide for trade, science, medicine and shipping. The stone (st) is a traditional British and Irish unit of mass, fixed at exactly 14 pounds (lb) by the UK Weights and Measures Act 1985. Because 1 pound = exactly 0.45359237 kilograms by the international yard-and-pound agreement of 1 July 1959, 1 stone = 14 × 0.45359237 = exactly 6.35029318 kilograms. This converter translates any mass between kilograms and stones in either direction, with the residual pounds (the "X st Y lb" form that British people actually use when talking about body weight) shown alongside, plus bonus read-outs in grams, US ounces and US short tons for freight and livestock contexts.

The page is designed for both everyday users (someone wanting to know their weight in the unit their UK GP uses) and professionals (vets, livestock auctioneers, boxing promoters, freight forwarders, rowing coaches, racing handicappers, agricultural buyers) who need a mathematically exact conversion traceable to the UK statute and the international yard-and-pound agreement.

How to Use

1. Kilograms (kg), type any non-negative number. This is the SI anchor: every other unit on the page is derived from this value, so entering kilograms and reading stones gives you the precise UK form ("11 st 4 lb", not "70 kg").
2. Stones (st), type any non-negative number of stones. The kilograms field updates live. Decimal stones are accepted ("11.5 st") and resolved into the canonical "X st Y lb" form automatically.
3. The result block shows kilograms, the decimal-stone equivalent, the canonical UK form ("11 st 4 lb"), total pounds, grams, US ounces and US short tons, every other unit you might need for downstream use.
4. Presets populate common values: 8 st (light), 10 st (average UK adult female), 11 st 4 lb (average UK adult male), 14 st (heavy), 17 st 4 lb (boxing heavyweight), 70 kg, 1200 kg (livestock, e.g. a Charolais bull).

The Formulae

The conversion rests on two exact definitions that have been stable since 1959 (pound) and 1350 (stone):

1 pound (avoirdupois)  = 0.45359237 kg   (exact, 1959 international agreement)
1 stone                = 14 lb           (exact, UK Weights and Measures Act 1985;
                                          statutory since the 14-lb wool stone of 1350)
1 stone                = 14 × 0.45359237 = 6.35029318 kg   (exact)
1 pound                = 16 oz           (US avoirdupois ounce)
1 kilogram             = 1000 g          (exact, SI definition of the kilogram)
1 US short ton         = 2000 lb         (exact, US customary)

Forward (kg → stones + pounds):

total_lb   = kg × (1 / 0.45359237) = kg × 2.2046226218487757
whole_st   = floor(total_lb / 14)
rem_lb     = total_lb − whole_st × 14

Reverse (stones + pounds → kg):

total_lb   = stones × 14 + pounds
kg         = total_lb × 0.45359237

Reverse (kg → stones only, decimal):

st_decimal = kg / 6.35029318

The factor 6.35029318 kg/st is exact, no rounding error accumulates. Display rounding is 5 decimal places for kilograms (about 0.01 g precision), which is finer than any practical bathroom or veterinary scale.

Worked Examples

Example 1, 70 kg (common adult body weight):

• total_lb = 70 / 0.45359237 = 154.32358 lb
• whole_st = floor(154.32358 / 14) = 11
• rem_lb = 154.32358 − 11 × 14 = 154.32358 − 154 = 0.32358 lb
• Canonical UK form: 11 st 0.3236 lb
• Decimal stones: 70 / 6.35029318 = 11.02311 st

Example 2, 11 st 4 lb (average UK adult male):

• total_lb = 11 × 14 + 4 = 154 + 4 = 158 lb
• kg = 158 × 0.45359237 = 71.66759 kg (rounded)
• g = 71,667.59 g
• oz = 158 × 16 = 2,528 oz
• US short tons = 158 / 2000 = 0.079 ton

Example 3, 1 stone exactly:

• kg = 1 × 6.35029318 = 6.35029318 kg (exact)
• lb = 14 lb (exact)
• oz = 224 oz (exact)
• short tons = 0.007

Example 4, 12 st 7 lb (boxing middleweight, traditional British class):

• total_lb = 12 × 14 + 7 = 168 + 7 = 175 lb
• kg = 175 × 0.45359237 = 79.37866 kg (rounded)
• short tons = 0.0875

Example 5, 0 kg (edge case):

• total_lb = 0, whole_st = 0, rem_lb = 0
• Canonical UK form: 0 st 0 lb = 0 kg = 0 g = 0 oz = 0 short tons

Example 6, 1 kg, working backwards:

• lb = 1 / 0.45359237 = 2.20462 lb (repeating decimal: 2.2046226218…)
• st_decimal = 1 / 6.35029318 = 0.15747 st (repeating)
• Canonical UK form: 0 st 2.2046 lb (≈ 0 st 2 lb 3.27 oz)

Example 7, 17 st 4 lb (boxing heavyweight, traditional British class):

• total_lb = 17 × 14 + 4 = 238 + 4 = 242 lb
• kg = 242 × 0.45359237 = 109.76935 kg (rounded)
• short tons = 0.121

Example 8, 1200 kg (livestock, Charolais bull):

• total_lb = 1200 / 0.45359237 = 2645.5471 lb
• st_decimal = 2645.5471 / 14 = 188.9677 st
• Canonical UK form: 188 st 11.7649 lb
• short tons = 1.3228

Example 9, 1 US short ton:

• lb = 2000 lb (exact)
• st_decimal = 2000 / 14 = 142.85714 st (repeating: 142 + 6/7)
• kg = 2000 × 0.45359237 = 907.18474 kg (rounded; the exact value is 907.1847386… kg)

Example 10, 100 kg (freight threshold):

• total_lb = 100 / 0.45359237 = 220.46226 lb
• st_decimal = 220.46226 / 14 = 15.74730 st
• Canonical UK form: 15 st 6.4623 lb

Where It Shows Up

• Body weight in the UK and Ireland, the canonical form for adults is "X st Y lb" rather than kilograms. Doctors' notes, prescription charts, hospital wristbands, weight-loss programmes (Slimming World, WW UK), personal-training apps and Apple Health UK all use stones. This converter is the fastest way to read those values in kilograms for international or scientific use.
• Boxing weight classes, British boxing retains traditional stone-and-pound thresholds for amateur and professional titles. Historic middleweight was set around 11 st 4 lb (≈ 72 kg), light-heavyweight around 12 st 7 lb (≈ 80 kg), heavyweight at "any weight" but typically over 14 st (≈ 89 kg). Modern British Boxing Board of Control (BBBofC) limits list classes from minimumweight (8 st 6 lb) to heavyweight (any weight over 14 st 4 lb).
• Wrestling weight classes, British wrestling, sumo (international), and amateur catch-as-catch-can still quote class boundaries in stones for some heritage tournaments. The British Wrestling Association has historically used 8 st, 9 st, 10 st, 11 st, 12 st, 13 st, 14 st thresholds for schoolboy and cadet divisions.
• Rowing eights, boat-class limits and individual rower weights are still sometimes quoted in stones; a "lightweight" men's eight averages around 12 st 6 lb (≈ 79 kg); an "open" heavyweight crew averages 14 st (≈ 89 kg). Henley Royal Regatta and the Boat Race have used stones for historical weight handicaps.
• Horse racing and equestrian sport, National Hunt (jump) racing has long used stone-and-pound descriptions for horse weights carried ("11 st 12 lb", "10 st 4 lb"). The Racing Post and the British Horseracing Authority (BHA) handicappers still publish weights in stones. A typical National Hunt hurdle race lists weights from about 10 st 2 lb upward.
• Livestock markets, Ireland's marts (cattle and sheep auctions) and smaller UK regional livestock markets still record animal weights in stones alongside the official metric figure. A finished steer of 80 st (508 kg) or a breeding ewe of 15 st (95 kg) are everyday numbers at an Irish mart.
• Agricultural produce and feed, older UK and Irish farm record books quote animal-feed weights, hay bale masses and grain sack weights in stones (e.g. "20 st of hay", "1 st of wool"). Converting to kilograms is necessary for modern subsidy forms, veterinary dosing and DEFRA returns.
• Freight, removals and shipping, international carriers convert between kg and lb constantly; UK domestic removals firms sometimes still quote a "20-st removal allowance" or a "5-st parcel". UK Royal Mail and Parcelforce use metric for postage rates but US-bound shipments are weighed in lb at the US end, so a reliable kg ⇄ st conversion sits in the middle.
• Older UK recipes and cookbooks, pre-1970s British recipes often quote ingredient weights in pounds and ounces (and sometimes stones for very large quantities like suet or root vegetables). Translating a Victorian recipe into modern grams requires a converter that handles both forms cleanly.
• Personal fitness apps with UK user bases, Strava, MyFitnessPal (UK region), Apple Health set to "Stones", Fitbit UK and Garmin Connect UK display body weight in stones + pounds and need a reliable kg conversion for storage and for sharing with international trainers.
• Medical dosing and pharmaceutical compounding, UK clinical pharmacists still receive patient weights in stones from older GP records; conversions to kg are needed for mg/kg dosing calculations, anaesthetic dosing and renal-function estimates.

Common Mistakes

1. Rounding 1 st to "6.35 kg", the exact value is 6.35029318 kg; rounding to two decimals (6.35) introduces ~0.029 kg error per stone, which accumulates for heavier people. For a 20-st person the error is ~0.58 kg, which matters for medication dosing. This converter displays 5 decimal places by default.
2. Confusing the international pound (0.45359237 kg) with the older "metric pound" of 500 g, the metric pound was an informal unit used briefly in 19th-century continental Europe. Modern statute (UK, US, Commonwealth) uses the international pound only. This converter uses 0.45359237 kg exactly.
3. Using 14 lb when the source actually means 16 lb, historically some US colonial sources used a "stone" of 16 lb for specific goods (wool in some colonies, butcher's meat in parts of Scotland). The UK statute fixes 14 lb; this converter uses that.
4. Treating stones and pounds as two independent fields, when entering "12 st 8 lb", the 8 lb is the remainder after subtracting whole stones (0 to 13.999…), not a separate independent weight. This converter resolves the canonical UK form correctly.
5. Forgetting that US medical scales report pounds, not stones, Americans often misread "11 st" as "11 pounds" or "11 kg". This converter labels the units explicitly and shows kilograms alongside so there is no ambiguity.
6. Using the troy pound (5,760 grains = 0.3732417216 kg) for body weight, the troy pound is for precious metals and pharmaceuticals, not people. This converter uses the avoirdupois pound (7,000 grains = 0.45359237 kg).
7. Confusing UK stones with the obsolete "wool stone" of 14 lb (which is the same!), actually the UK "stone" and the "wool stone" are the same 14-pound unit, fixed in 1350 by Edward III's Statute of the Pillory and confirmed by the Weights and Measures Act 1985. There is no separate "wool stone" or "London stone" with a different value.
8. Assuming "stones and pounds" is the same in Ireland and the UK, both use the same definitions (1 st = 14 lb) by virtue of the Metric Act 1967 (Ireland) and historical continuity. Ireland formally uses metric (kg) for trade but retains stones for body weight and livestock. The conversion factors are identical.
9. Off-by-one when entering "11 stone 4 pounds", the 4 is residual after 11×14=154, so the total is 158 lb, not 154 lb, this converter resolves the canonical form correctly, but users typing 154 + 4 = 158 in their head should see the same result on screen.
10. Adding stones to kilograms without first converting, the most common arithmetic mistake is "70 kg + 11 st" (treating them as if they were the same unit). They are not; always convert one to the other first. This converter shows both at once so the comparison is direct.

Frequently Asked Questions

How many kilograms are in a stone? One stone equals exactly 6.35029318 kilograms. The figure follows from two exact definitions: the UK Weights and Measures Act 1985 fixes 1 stone = 14 pounds, and the international yard-and-pound agreement of 1 July 1959 fixes 1 pound (avoirdupois) = 0.45359237 kilograms. Therefore 14 × 0.45359237 = 6.35029318 kg, with no rounding error.

How many stones are in a kilogram? One kilogram equals approximately 0.15747304 stones (the reciprocal of 6.35029318). The exact value is the repeating decimal 0.15747304441776972…, which never terminates. For practical use, 1 kg ≈ 0.157473 st or, in mixed units, 1 kg ≈ 0 st 2 lb 3.27 oz.

How do I convert kilograms to stones manually? Divide the kilograms by 6.35029318 to get decimal stones, then split into whole stones and residual pounds: whole_st = floor(decimal_st); rem_lb = (decimal_st − whole_st) × 14. Example: 80 kg / 6.35029318 = 12.5981 st → 12 st 8.3760 lb. The two-step approach avoids the rounding traps of single-multiply shortcuts.

How do I convert stones to kilograms manually? Multiply stones by 14 to get pounds, then multiply by 0.45359237 to get kilograms. Shortcut: multiply stones by 6.35029318. Example: 11 st × 6.35029318 = 69.85322 kg. The shortcut is mathematically identical because 14 × 0.45359237 = 6.35029318 exactly.

Why do British people use stones for body weight? The stone was the traditional English unit of weight (originally a stone of wool = 14 lb, fixed by law in 1350 under Edward III). Even after metrication in the 1970s and 1980s, the stone survived as the colloquial unit for body weight in the UK and Ireland, partly because "11 st 4 lb" feels more natural to a British ear than "70 kg" or "158 lb" when describing a person's size. It is also the unit most British bathroom scales default to, even in 2026.

Is the stone used in Ireland? Yes. Ireland shares the UK definition (1 st = 14 lb) by virtue of the Metric Act 1967 and historical continuity. The stone is colloquial for body weight in Ireland, even though metric (kg) is the formal system for trade and veterinary records. Irish livestock marts still record cattle and sheep weights in stones alongside the official metric figure.

How accurate is this converter? Mathematically exact at the 6.35029318 kg/st level, the underlying factor is the product of two exact statutory definitions (14 × 0.45359237). Display rounding is to 5 decimal places for kilograms (about 0.00001 kg = 0.01 g precision), finer than any practical bathroom or veterinary scale. All definitions (lb, st, kg) come from the UK statute and the 1959 international agreement, no approximation.

What is the boxing heavyweight limit in stones? Historically, British professional boxing treated heavyweight as "any weight" above about 14 st 4 lb (≈ 90.7 kg) for title fights. The British Boxing Board of Control (BBBofC) currently sets the heavyweight limit at 200 lb (90.72 kg ≈ 14 st 4.72 lb) for weigh-in, with no upper limit for the actual bout. Earlier traditional limits ranged from 12 st 7 lb (middle) to 13 st 6 lb (light-heavy) to 14 st 4 lb (heavy).

How heavy is a stone in livestock terms? A "stone" of wool, hay, root vegetables or animal feed has been a 14-pound measure since medieval times. For livestock, a finished steer at market typically weighs 70-100 st (445-635 kg); a breeding ewe 10-18 st (64-114 kg); a market hog 8-14 st (51-89 kg). A "stone" of wool at a UK wool auction is exactly 14 lb (6.35 kg), though modern wool is sold by the kg or by the tonne.

Is 1 stone the same as 14 pounds in every country? Almost. The UK, Ireland, Australia, New Zealand, Canada, South Africa and the English-speaking Commonwealth all use the 14-pound stone. Some historical sources cite 16-pound stones for specific trades (wool in the early American colonies, butcher's meat in some Scottish burghs), but the modern statutory definition is 14 lb everywhere it survives as a recognised unit. This converter uses 14 lb exactly.

Can I use this for medical or pharmaceutical purposes? The conversion is mathematically exact and uses authoritative sources (UK Weights and Measures Act 1985, international yard-and-pound agreement 1959, NIST SP 811). For medication dosing, always verify with a clinician and follow the dose calculation as written in the prescription, some drugs use ideal body weight (IBW) or adjusted body weight rather than total body weight, and this converter does not compute those. For veterinary dosing, the same caveat applies: total body weight is the input, but dose-by-weight-surface-area (mg/m²) requires an extra formula this converter does not perform.

What's the heaviest "stone" weight a person has been recorded at? The heaviest medically validated adult human weight on record is around 635 kg (1,400 lb ≈ 100 st), recorded by Jon Brower Minnoch (USA, 1978). Converted: 1,400 lb ÷ 14 = 100 st exactly. This converter handles any non-negative input.

Why does the converter show both kg and stones? Body weight in the UK is canonically given in stones and pounds, but most international scientific, medical and commercial contexts require kilograms. Showing both lets users verify their own knowledge ("I know I weigh about 70 kg, does the stone-and-pound version match?") and use the result in any downstream application without an extra conversion step. The converter also displays grams (for very small masses like pharmaceuticals), pounds (for US shipment), ounces (for food packaging) and US short tons (for very heavy freight).

How do I convert a person's weight from kg to UK stones quickly? Divide by 6.35 for a quick mental estimate (within 0.05%). For the exact canonical form, divide by 6.35029318 to get decimal stones, then split into whole stones and residual pounds. Example: 75 kg / 6.35029318 = 11.81018 st → 11 st 11.3425 lb (canonical UK form). The "× 2.2 / 14" mental shortcut is roughly 0.2% off, which is fine for casual use but not for clinical records.

can the Kilograms to Stones Converter, 1 st = 14 lb = 6.35029318 kg be used for professional or commercial purposes? yes, the Kilograms to Stones Converter, 1 st = 14 lb = 6.35029318 kg provides mathematically correct results that are suitable for professional, commercial, and educational use. For the Kilograms to Stones Converter, 1 st = 14 lb = 6.35029318 kg, For the Kilograms to Stones Converter, 1 st = 14 lb = 6.35029318 kg, For high-stakes applications (medical, legal, financial), verify results with a domain expert. For the Kilograms to Stones Converter, 1 st = 14 lb = 6.35029318 kg, the Kilograms to Stones Converter, 1 st = 14 lb = 6.35029318 kg formulas used are well-established and validated against reference standards.

For the Kilograms to Stones Converter, 1 st = 14 lb = 6.35029318 kg, How often are the underlying formulas updated? For the Kilograms to Stones Converter, 1 st = 14 lb = 6.35029318 kg, the Kilograms to Stones Converter, 1 st = 14 lb = 6.35029318 kg formulas are based on established scientific, mathematical, or industry-standard references and rarely require updates. When standards change (e.g., new physical constants, revised trade definitions, updated medical guidelines), this calculator is updated to reflect the current authoritative source. For the Kilograms to Stones Converter, 1 st = 14 lb = 6.35029318 kg, For the Kilograms to Stones Converter, 1 st = 14 lb = 6.35029318 kg, Each calculator's references section lists the specific sources used.

References

1. UK Weights and Measures Act 1985 (c. 72), Schedule 1, units of measurement lawfully usable for trade. Published by The Stationery Office, London.
2. International yard-and-pound agreement of 1 July 1959 among the US, UK, Canada, Australia, New Zealand and South Africa, fixed 1 yard = 0.9144 m exactly and 1 lb (avoirdupois) = 0.45359237 kg exactly. Federal Register, US National Archives.
3. For the Kilograms to Stones Converter, 1 st = 14 lb = 6.35029318 kg, NIST Special Publication 811 (2008), Appendix B.8, Recommended Conversion Factors for Use by Federal Agencies. National Institute of Standards and Technology, US Department of Commerce.
4. Metric Act 1967 (Ireland), confirms Irish use of metric units for trade while preserving customary units (including the stone) for colloquial use.
5. BIPM SI Brochure (9th ed., 2019), §2.3.3, definition of the kilogram via the fixed value of Planck's constant (since 2019) and historical continuity with the international prototype.
6. British Boxing Board of Control (BBBofC), current rules and weight-class limits for professional boxing in the UK, including stone-based historical thresholds.
7. The Weights and Measures (Equivalents for Dealing with Drugs) Order 1970 (SI 1970/1897), UK statutory instrument defining the pound in grams (454 g, rounded) for pharmaceutical contexts.
8. British Horseracing Authority (BHA), Pattern and Listed race weight allowances, traditionally published in stones and pounds for National Hunt racing.

Also try these free tools:

• Pounds to Stones Converter, stones + pounds ↔ kg with the residual pounds shown
• Kilograms to Pounds Converter, kg ↔ lb with grams and ounces read-outs
• Stones to Kilograms Converter, sister converter for the same UK units
• Body Mass Index Calculator, uses kg internally; pair with this converter
• Weight Converter, broader multi-unit (mg, g, kg, oz, lb, st) conversion