Grams, kilos and pounds: the weight conversions that matter
The rule of thumb "kilograms × 2 = pounds" is close — but wrong enough to matter. The real factor is 2.20462, so on a 30 kg suitcase the shortcut undercounts by about 6 lb, which is exactly the margin airlines charge for. The tool above uses the exact constants and converts in both directions as you type, including the units people actually hit: grams and ounces for recipes, stone and pounds for body weight, tonnes and tons for freight.
Mass versus weight: why the words differ
In everyday speech the two are interchangeable, but they are different physical ideas. Mass is how much matter an object contains and never changes, wherever it is. Weight is the gravitational pull on that mass — the same 60 kg astronaut weighs about 10 kg-equivalent on the Moon. Scales in daily life effectively measure mass in units like kilograms and pounds, so the distinction only really matters in physics and space travel.
Baggage, body weight and gym plates: three worked examples
- Airline luggage: A 23 kg checked-bag limit is 50.7 lb. Your 48 lb suitcase is 21.77 kg — under the limit, but only just.
- Body weight: A UK person weighing 12 stone 6 lb is 174 lb — multiply by 0.453592 for 78.9 kg. The "12 stone" habit is why the tool includes stone.
- Gym plates: An Olympic bar with two 25 kg plates is 20 + 50 = 70 kg, or 154.3 lb. If the gym labels plates in pounds instead, 45 lb plates give a 155 lb bar.
Everyday conversion factors
| From Unit | To Unit | Value |
|---|---|---|
| Kilograms (kg) | Pounds (lb) | 2.20462 |
| Pounds (lb) | Kilograms (kg) | 0.453592 |
| Grams (g) | Ounces (oz) | 0.035274 |
| Stone (st) | Pounds (lb) | 14 |
| Ounces (oz) | Grams (g) | 28.3495 |
| Tonne (t) | Kilograms (kg) | 1,000 |
Where the specialist units show up
- Carat (ct): Gemstones. One carat is exactly 200 mg (0.2 g) — a 1-carat diamond is therefore 0.2 g.
- Grain (gr): Ammunition, gunpowder and arrows. One grain is exactly 64.79891 mg, originally tied to a single cereal seed.
- Troy ounce: Gold and silver. Heavier than the everyday (avoirdupois) ounce — 31.1035 g vs 28.3495 g — which is why a "1 oz" gold bar weighs more than 28 g. This tool uses the everyday ounce; precious-metals dealers work in troy ounces.
- Short vs long ton: The US short ton is 2,000 lb, the UK long ton is 2,240 lb, and the metric tonne is 1,000 kg (≈2,204.6 lb). Freight contracts always specify which one.
Weight questions that keep coming up
How many pounds make up one stone?
Exactly 14. Someone weighing 10 stone weighs 140 lb, or 63.5 kg.
Is "times 2" good enough for kilograms to pounds?
For a rough sense, yes. The exact factor is 2.20462, so "×2" undercounts by about 9%. At airport weight limits or for precise dosing, use the tool — the difference is real.
Why do I see both kg and lb on the same product?
Dual labelling exists because the US uses pounds while most of the world uses kilograms. The tool's job is to reconcile the two when a listing only gives one.
How small do the units go?
Down to micrograms (one-millionth of a gram), the scale used in pharmacology for vitamin doses and compounding. The tool converts microgram, milligram and gram together with the everyday units.