What this tool does
This converter moves between kilograms, pounds, and stone + pounds in any of the six directions. Type a value, pick a conversion pair from the dropdown, and the result appears immediately in your browser — nothing is sent to a server.
Stone + pounds is the standard way body weight is expressed in the UK: a person weighs, say, 11 st 3 lb rather than 157 lb or 71.2 kg. The tool always breaks stone-and-pound output into the integer stone count and the remaining decimal pounds, matching what a GP or pharmacy printout shows.
Mass or weight — does it matter here?
Strictly, a kilogram measures mass — how much matter something contains — while "weight" is the force gravity exerts on that mass, which technically varies with location (you'd read slightly lighter on a mountain than at sea level, and far lighter on the Moon). Scientifically the two are different quantities with different units: mass in kilograms, weight in newtons. Everyday usage collapses this distinction, and reasonably so — bathroom scales, luggage limits, and food labels all report mass in kilograms and call it "weight," and gravity at any point on Earth's surface is close enough to constant that the two track each other for practical purposes. This converter, like every scale you've ever stood on, converts mass. Nothing below depends on the physics distinction; it's just worth knowing the word "weight" is doing double duty.
The conversions
One kilogram is defined as 1 000 g in the International System of Units. The pound is defined by the 1959 international agreement as exactly 0.45359237 kg, which makes 1 kg = 1 ∕ 0.45359237 ≈ 2.20462262185 lb. The stone is exactly 14 lb by UK statute.
To convert stone + lb to kilograms, first convert the whole value to pounds (stone × 14 + lb) and then multiply by 0.45359237.
Worked example
Take 70 kg, a typical adult body weight. Multiplying by 2.20462262185 gives 70 × 2.20462262185 = 154.3236 lb. Dividing the pound value by 14 and taking the integer part gives 11 st, with 154.3236 − (11 × 14) = 0.3236 lb remaining. So 70 kg = 11 st 0.3236 lb.
One country, two systems: trade went metric, bodies didn't
The stone as a unit of trade dates to medieval England, where it was used for wool, meat, and butter, and Parliament standardised it at 14 lb in the Weights and Measures Act 1835. Trade is where metrication actually landed: since 1 January 2000, UK law has required loose goods sold by weight — fruit, veg, meat cut to order, cheese off the block — to be priced and measured in kilograms and grams, with imperial allowed only as a supplementary label alongside the metric figure. Walk into a UK greengrocer today and the scale reads in grams.
Body weight never made that jump. It sits outside the "legal for trade" rules that pushed groceries metric, so it kept the older unit by default: stone remains what most UK adults think in, what NHS records display alongside kilograms, and what bathroom scales sold in Britain are calibrated to show first. The result is a country that buys its potatoes in kilograms and weighs itself in stone — two systems, split cleanly along a line that has nothing to do with which unit is "more modern" and everything to do with which sales were regulated and which weren't. There's more on how that split happened in our guide to why Britain weighs in stone.
Pounds alone (without stone) remain standard for body weight in the United States and in most clinical contexts there, while continental Europe uses kilograms exclusively for both trade and body weight.
Common uses
- Body weight: checking a kg figure from a GP, scales, or a fitness app against the stone + lb reading most UK adults think in.
- Luggage: airline allowances are often quoted in kilograms; US carriers may use pounds.
- Recipes and food labels: older British recipes quote ingredients in pounds and ounces; modern packaging uses grams, the metric side of the same trade rules covered above.
- Gym equipment: weight plates are marked in both kg and lb depending on country of manufacture.
Frequently asked
How many pounds are in a stone?
Exactly 14 lb. One stone = 14 lb is a statutory definition, not an approximation, so all stone–pound conversions are exact with no rounding involved.
Is the pound-to-kg conversion exact?
Yes. The 1959 international yard and pound agreement fixed 1 lb = 0.45359237 kg precisely. The reciprocal (1 kg ≈ 2.20462262185 lb) is a repeating decimal, so the converter rounds to 4 decimal places.
Is weight the same as mass?
Not to a physicist — mass (kg) is how much matter you have, weight is the gravitational force on it (newtons) — but for any conversion on this page, and on every scale you'll ever step on, "weight" means mass. The distinction only bites in physics and spaceflight, not in the kitchen or the GP's surgery.
Why do UK shops sell in kilograms but people weigh themselves in stone?
Because only trade weights were legally required to go metric. Since 2000, loose goods sold by weight must be priced in kilograms; body weight was never covered by that rule, so stone survived as the everyday default. See our guide to why Britain weighs in stone for the fuller history.