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Weight Converter
Convert kilograms, pounds, stone and ounces, and see why a scale in kg is more precise than one in lb.
On 23 July 1983, an Air Canada Boeing 767 ran out of fuel mid-flight and had to glide, engines dead, into a disused airstrip near Gimli, Manitoba. The cause traced back to a single unit conversion error, using pounds where the calculation needed kilograms.
The Gimli Glider, in short
Canada was mid-transition to metric units, and the 767 was one of the first Air Canada aircraft with metric fuel gauges reading in kilograms. Ground crew, manually calculating the fuel load after an instrument fault, used a conversion factor of 1.77 — pounds per litre — instead of the correct 0.803, kilograms per litre. The plane took off with less than half the fuel it needed and ran dry at 41,000 feet. The captain, a glider pilot in his spare time, dead-sticked it to a safe landing with no injuries. It remains one of the most cited cautionary tales in aviation about what a single wrong conversion factor can do.
Mass and weight are not actually the same thing
Strictly, mass is how much matter something contains and weight is the force gravity exerts on that mass, measured in newtons. On Earth the distinction rarely matters, which is why “weight” and “mass” get used interchangeably and a kitchen scale happily reports kilograms as if it were measuring weight. The distinction becomes real the moment gravity changes — an astronaut’s mass stays constant on the Moon, but their weight drops to about a sixth of what it is on Earth.
Weight units compared
| Unit | In kilograms | Where it is used |
|---|---|---|
| 1 kilogram (kg) | 1 | The global standard for body and product weight |
| 1 pound (lb) | 0.4536 | US everyday weight, also used informally in the UK |
| 1 stone (st) | 6.35 | Body weight in the UK and Ireland only |
| 1 ounce (oz) | 0.02835 | Cooking measures, postage, precious metals |
The stone is a genuinely local unit
- It is used for body weight in the UK and Ireland, essentially nowhere else.
- One stone is defined as exactly 14 pounds, or about 6.35 kg.
- Even within the UK, medical and scientific contexts use kilograms, while everyday conversation still runs in stone and pounds.
- Outside the UK and Ireland, “stone” as a weight unit is essentially unknown, which is a common source of confusion for visitors reading a UK weight chart.
Weight conversion questions
How many pounds are in a kilogram?
About 2.205. So a 70 kg adult weighs roughly 154 lb, a figure worth rounding to memory since the exact multiplier, 2.20462, rarely needs to be that precise outside a lab.
How many pounds are in a stone?
Exactly 14. A person who weighs 11 stone weighs 154 lb, which conveniently is also close to the 70 kg example above — those three figures (70 kg, 154 lb, 11 stone) describe the same weight.
Is weight the same thing as mass?
Technically no. Mass is an intrinsic property of matter, while weight is the force gravity exerts on that mass. On Earth’s surface the two track each other closely enough that everyday language treats them as interchangeable, but they diverge anywhere gravity differs, such as on the Moon.
What caused the Gimli Glider fuel shortage?
Ground crew used the wrong conversion factor when calculating how much fuel to load, applying a pounds-per-litre figure instead of the correct kilograms-per-litre figure during Canada’s transition to metric measurements. The aircraft took off with under half the fuel it needed for the flight.
Why do UK bathroom scales sometimes show stone and pounds together?
Because body weight in the UK and Ireland is still conventionally discussed in stone and pounds rather than kilograms, even though kilograms are the metric standard used almost everywhere else and in UK medical records.
