Hong Life CalculatorsUnderstanding the weight converter — concept and principle
This converter changes a mass between kilograms, grams, milligrams, pounds, ounces and stone. It is useful for body weight on foreign scales or medical forms, recipes from US or UK cookbooks, gym plates, luggage allowances and parcel postage. Enter a value and pick the units; the page also lists the same weight in every other unit.
How it is calculated
Each unit is stored as an exact number of kilograms:
- 1 lb = 0.45359237 kg
- 1 oz = 1/16 lb = 0.028349523125 kg (28.349523125 g)
- 1 stone = 14 lb = 6.35029318 kg
- 1 g = 0.001 kg; 1 mg = 0.000001 kg
Result = value × (kg per "from" unit) ÷ (kg per "to" unit). Going the other way, 1 kg = 1 ÷ 0.45359237 ≈ 2.20462262 lb.
The principle
The pound used today is the international avoirdupois pound. In 1959 the US, UK and other Commonwealth countries agreed to define it as exactly 0.45359237 kg, ending small differences between national pounds. Since then the pound is simply a fixed fraction of the kilogram, and the kilogram itself has been defined since 2019 through the Planck constant. Ounces and stone are fixed multiples of the pound, so every factor in this calculator is exact; only the display is rounded.
Worked example
Default: 150 pounds to kilograms.
- Multiply by the pound factor: 150 × 0.45359237 = 68.0388555 kg.
- Result: 150 lb = 68.0388555 kg, about 68.0 kg.
- Other units: 68,038.8555 g; 150 × 16 = 2,400 oz; 150 ÷ 14 = 10.71428571 stone (10 st 10 lb).
How to read the result
A quick mental check: kilograms are a bit less than half the pounds (divide by 2.2), and pounds are a bit more than double the kilograms. For body weight, one decimal place in kg is plenty; for medicine doses or baking, keep grams. UK body weight is often quoted in stone and pounds, so 10.71 stone is usually written as 10 st 10 lb.
Common mistakes
- Using 2.2 or 0.45 for precise work; the small error grows with large values.
- Mixing avoirdupois ounces with troy ounces (31.1034768 g) used for gold and silver.
- Confusing weight ounces (oz) with fluid ounces (fl oz), which measure volume.
Frequently asked questions
How many pounds are in a kilogram?
About 2.20462262 lb.
How many grams are in an ounce?
Exactly 28.349523125 g, about 28.35 g.
How do I convert 10.71 stone into stone and pounds?
Keep the 10 stone, then multiply the 0.71 by 14 to get about 10 lb, so 10 st 10 lb.
Is weight the same as mass?
Strictly, kg and lb measure mass; everyday "weight" means mass, which is what this calculator converts.
Sources: NIST Special Publication 811 (2008), Appendix B · BIPM, SI Brochure, 9th edition, 2019 (definition of the kilogram)