Weight and mass unit conversion
On Earth, weight and mass are often used interchangeably in daily life; science treats them differently.
Unit converter
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| From | To | Multiply by |
|---|---|---|
| 1 kilogram (kg) | grams (g) | 1000 |
| 1 kilogram (kg) | pounds (lb) | 2.20462 |
| 1 pound (lb) | kilograms (kg) | 0.453592 |
| 1 pound (lb) | ounces (oz) | 16 |
| 1 ounce (oz) | grams (g) | 28.3495 |
| 1 gram (g) | milligrams (mg) | 1000 |
| 1 stone (st) | pounds (lb) | 14 |
| 1 stone (st) | kilograms (kg) | 6.35029 |
| 1 metric ton (t) | kilograms (kg) | 1000 |
| 1 US ton (short) | pounds (lb) | 2000 |
| 1 US ton (short) | kilograms (kg) | 907.185 |
| 1 UK ton (long) | pounds (lb) | 2240 |
| 1 carat (ct) | grams (g) | 0.2 |
Notes
- Jewelry carat (ct) is mass; diamond “carat” in gems is the same unit.
- US short ton ≠ metric tonne.
The kilogram and the 2019 redefinition
The kilogram is the SI base unit of mass, and until 2019 it was the last one defined by a physical object: a platinum–iridium cylinder kept at Sèvres, France, known as the International Prototype Kilogram. Since 20 May 2019 it has instead been defined by fixing the Planck constant at exactly 6.62607015 × 10⁻³⁴ joule-seconds, so any laboratory with a Kibble balance can realize the kilogram directly rather than copy it from one artefact. Every other metric mass unit on this sheet derives from it by powers of ten: 1 kilogram = 1000 grams, 1 metric ton = 1000 kilograms, and a gram is 1000 milligrams, exactly as the conversion rows show.
Avoirdupois vs troy ounces
Not all ounces are equal. The avoirdupois ounce used in cooking and everyday commerce weighs 28.3495 grams, and sixteen of them make one pound, matching the sheet's rows. Precious metals use the heavier troy ounce of 31.1035 grams, grouped into troy pounds of only 12 ounces — which is why a gold or silver price quoted per ounce looks higher than a kitchen-scale conversion would suggest. Gemstones sidestep the confusion with the carat, exactly 0.2 grams, listed separately in the table. Before converting, always check which ounce you hold: a troy ounce is about 9.7% heavier than an avoirdupois ounce, and on bullion or jewelry that error compounds fast.
Body weight: stone, pounds and the jin
Body weight habits differ sharply by region. In the UK and Ireland people still give their weight in stone — 14 pounds, about 6.35 kilograms — usually paired with leftover pounds, as in "11 st 4 lb". The United States uses pounds directly, keeping this sheet's 1 lb = 0.453592 kg row in constant use. In China and much of East Asia, the traditional jin (catty) survives in markets and recipes at exactly 500 grams — precisely half a kilogram — so a person of "150 jin" weighs 75 kg. None of these units are SI, but each converts exactly: 1 stone = 6.35029 kg per the table.
Practical anchors: luggage and baking
Two everyday anchors make the numbers concrete. First, checked luggage: most airlines cap one checked bag at 23 kg — the familiar 50 lb limit — so multiplying by the sheet's 2.20462 factor tells you instantly whether a suitcase is overweight. Second, baking: recipes that measure flour by volume drift badly, because a "cup" of flour can weigh roughly 120–130 g depending on how it is scooped; professional bakers therefore weigh in grams or ounces, units this sheet converts exactly. Water is the simplest reference of all — one litre weighs almost exactly 1 kg — while gems and precious metals keep their own units, the carat and troy ounce covered above.
Frequently asked questions
- How many pounds are in a kilogram?
- One kilogram ≈ 2.20462 pounds; conversely, one pound is 0.453592 kg.
- How many grams are in an ounce?
- One ounce ≈ 28.35 grams, and one pound contains exactly 16 ounces.
- How much is one stone in kilograms?
- One stone equals 14 pounds ≈ 6.35 kg; it is still used for body weight in the UK and Ireland.