History & Background
The kilogram was originally defined in 1795 as the mass of one liter of pure water at 4 °C. From 1889 to 2019 it was defined by the International Prototype of the Kilogram (a platinum-iridium cylinder kept in Sèvres, France). In 2019 the SI was redefined and the kilogram is now fixed by the Planck constant, h.
Conversion Formulas
1 kg = 2.20462 lb = 35.274 oz1 lb = 0.453592 kg = 16 oz1 oz = 28.3495 g1 stone (UK) = 14 lb = 6.35029 kg1 tonne = 1,000 kg = 2,204.62 lb
Common Values
- 70 kg ≈ 154.3 lb (average adult)
- 1 lb butter = 453.6 g (4 sticks)
- 5 lb bag of flour = 2.27 kg
- 100 g chocolate ≈ 3.53 oz
- 1 oz silver = 28.35 g
- 1 stone = 6.35 kg (UK body weight)
Common Uses
- Kitchen and baking — converting pound recipes to a metric scale
- Fitness and bodybuilding — tracking weight in kg or lb
- Shipping — package weight limits
- Precious metals — ounces (troy and avoirdupois)
- Medication doses (mg / g)
Practical Tips
- Precious metals use the troy ounce (31.1035 g), not the regular avoirdupois ounce (28.35 g).
- UK body weight is still commonly given in stones and pounds.
- For postal weight rules always round up — never down.
Frequently Asked Questions
How many pounds in a kilogram?
1 kg = 2.20462 lb. So 50 kg ≈ 110.2 lb.
How many grams in an ounce?
28.3495 g (avoirdupois). For precious metals, 1 troy oz = 31.1035 g.
What is "weight" vs "mass"?
Mass is the amount of matter (kg). Weight is the gravitational force on that mass (newtons). On Earth the two are proportional, so colloquial usage treats kg as weight.
How heavy is a stone?
1 stone = 14 lb = 6.35 kg. Used in the UK and Ireland for body weight.
How many kg in a metric tonne?
1 tonne = 1,000 kg. The US "short ton" is 907.185 kg; the UK "long ton" is 1,016 kg.