How this instrument works
Since 1 July 1959, the avoirdupois pound has been defined as exactly 0.45359237 kilograms — not measured, defined. Six nations signed the international yard and pound agreement, and from that date every conversion between metric and avoirdupois mass became pure algebra. One kilogram is 1 ⁄ 0.45359237 = 2.2046226218 pounds, with as many further digits as you care to carry. There is no experimental uncertainty in this instrument at all; the only error you can introduce is rounding.
The avoirdupois chain hangs off the pound in fixed whole-number steps: 16 ounces make a pound, and 14 pounds make a stone. So the sheet computes each output from the same anchor — pounds are kilograms times 2.2046226218, ounces are sixteen times that, stone is a fourteenth of it, and grams are simply kilograms times 1000, the metric prefix doing the work. Because every link in the chain is exact, converting back and forth loses nothing but the digits you choose to drop.
A practical note on the shortcut everyone learns: 2.2 pounds per kilogram runs about 0.21% low. Fine for groceries, noticeable at scale — over a 120 kg shipment the shortcut misplaces more than half a pound. This sheet keeps the full factor so the choice of precision stays yours.
- Type your figure into the Mass field — the sheet opens with 1 kg as a worked reference.
- Pick the unit you measured in from the menu: grams, kilograms, ounces, pounds, stone, or tonnes.
- Read the four output rows — Pounds, Ounces, Grams, and Stone — which update as you type.
- Copy the log line if you want a compact one-line record of the conversion for your notes.
Worked example — the one-kilogram bag of sugar
Take the standard 1 kg bag of sugar. Pounds: 1 × 2.2046226218 = 2.204623 lb. Ounces: sixteen to the pound, so 2.2046226218 × 16 = 35.273962 oz. Grams: 1 × 1000 = 1000 g, the metric prefix doing all the work. Stone: 2.2046226218 ⁄ 14 = 0.157473 st — a reminder that stone is a unit for people, not groceries.
Run it in reverse to see the definition itself: enter 0.45359237 kg and the Pounds row reads exactly 1, the Ounces row exactly 16. That is not a coincidence the sheet found — it is the 1959 definition coming back out unchanged, which is a decent quick check that any converter you use is honest.
Questions
How many pounds are in a kilogram?
2.2046226218 — usually quoted as 2.20462, or 2.2 in the kitchen. The value is exact algebra, not measurement: the pound is defined as 0.45359237 kg, so a kilogram is one divided by that, carried to as many digits as the job needs. For body weight, two decimals are plenty; for freight paperwork, keep four or more.
Why is the pound exactly 0.45359237 kg?
Because six countries — the United States, United Kingdom, Canada, Australia, New Zealand, and South Africa — agreed to fix it there in the international yard and pound agreement, effective 1 July 1959. Before that, national pounds differed by a few parts per million, enough to bother precision industry. The agreed figure was chosen to sit close to all of them, and it has been the single legal pound ever since.
What is a stone, and who still uses it?
A stone is 14 pounds, or exactly 6.35029318 kg. It survives almost entirely in Britain and Ireland as the customary unit for body weight — someone is '11 stone 4' rather than 158 pounds. It is not used for trade, and the United States dropped it long ago, which is why American scales read in pounds and British bathroom scales often read in stone.
Is a fluid ounce the same as the ounce here?
No. This sheet converts mass, and its ounce is the avoirdupois ounce — a sixteenth of a pound, about 28.3495 g. A fluid ounce is a volume, roughly 29.57 ml in the US and 28.41 ml imperial, and how much a fluid ounce weighs depends on what is in the glass. Recipes that mix the two are the source of much kitchen grief.
Is multiplying by 2.2 accurate enough?
It depends on the stakes. The shortcut sits 0.21% below the true factor of 2.2046226218, so a 70 kg person becomes 154.0 lb instead of 154.3 — nobody minds. Scale it up and the gap grows: a 1000 kg pallet comes out 4.6 lb light. Use 2.2 for conversation, and the full factor whenever the number goes on paper.