Weight Converter

Why 23 kg and 32 kg, and why nobody will negotiate the second one

The two numbers on a baggage policy do different jobs. 23 kg is a fare boundary: it is where the airline starts charging you, and it is negotiable in the sense that money makes it go away. It also happens to land almost exactly on 50 lb, which is how the same limit gets written in both systems on the same website.

32 kg is not a fare boundary. It is a manual-handling ceiling, and it is there for the person in the hold rather than for you. A baggage handler works a shift lifting a bag every few seconds, often bent double in an aircraft hold with no room to straighten up, and occupational health rules in most countries cap what one person may lift repeatedly in that posture. Above 32 kg a bag stops being baggage and becomes cargo, handled by two people or by machine, which is a different process with a different cost. That is why airlines will happily sell you a second bag and will simply refuse the 35 kg one at any price. Turning up with an overweight case is not a haggling situation; it is a repacking situation, and the queue behind you knows it.

The 70 lb figure you see on American carriers is the same ceiling written the other way: 70 lb is 31.75 kg. 50 lb is 22.68 kg. The pairs are not conversions of each other, they are two roundings of the same underlying limit, which is why a bag can pass at 23.0 kg in Europe and be flagged at 50.7 lb in the United States.

The limits you meet most often

These are the common thresholds, not a quote. Allowances vary by airline, route, cabin, fare type and status, and low-cost carriers change them more often than anyone else. The only number that matters is the one on your own booking — this list is for knowing which wall you are near.

Weigh the bag at home. Bathroom scales work: stand on them holding the case, stand on them without it, subtract. A luggage scale is better and costs less than one excess-baggage charge.

The stone, explained for everyone outside Britain and Ireland

A stone is 14 pounds, or 6.35029318 kg. It is used for one thing only — the weight of a person — and a Briton who says "eleven stone six" means 160 lb, or 72.6 kg. Nobody in Britain weighs luggage, flour or a parcel in stones. The unit lives on in two places: body weight and the weight of a boxer.

It was once literally a stone, a physical lump kept at the market as a standard, and its weight depended on what you were weighing with it. The wool stone was 14 lb; the meat stone was 8. The Weights and Measures Act of 1835 settled it at 14 for everything, and the wool merchants won. Fourteen is a bad number to divide by, which is why the unit never travelled.

• Never write it as a decimal. "11.5 stone" means 11 stone 7 pounds, because half of 14 is 7. People read it as 11 stone 5 and are two pounds out.
• It does not pluralise in use. "Eleven stone six", not "eleven stones six". The plural exists, but not when you are stating a weight.
• An American medical chart will be in pounds alone. 160 lb, not 11 st 6. Converting badly between the two is the classic error in a translated health form.

The pound is defined from the kilogram, not the other way round

Since the international yard and pound agreement of 1959, the avoirdupois pound has been exactly 0.45359237 kg. Not approximately — exactly, by definition. Every imperial weight is now a defined fraction of a metric one, which means every conversion on this page is exact to the digits shown and the only rounding happens on display.

Two traps worth knowing. The troy ounce, used for gold, silver and platinum, is 31.1034768 g, while the ordinary avoirdupois ounce is 28.349523125 g — about 10% heavier, which is a large error to make on a bullion price. And the fluid ounce is a unit of volume, not of weight, and the US and imperial versions differ from each other as well: 29.57 ml against 28.41 ml. A recipe that says "8 oz of flour" and one that says "8 fl oz of milk" are measuring different things.

The conversions worth memorising

The mental version: kilograms to pounds, double it and add ten per cent. 70 kg becomes 140 plus 14, which is 154 — the true answer is 154.3. Pounds to kilograms, halve it and take off ten per cent: 160 lb becomes 80 minus 8, which is 72, against a true 72.6.