Pounds and kilograms
The avoirdupois pound is exactly 0.45359237 kilograms (1959 agreement) and contains 16 ounces. Body weight, food and product weights in the US, and body weight alongside stone in the UK, use pounds.
The kilogram is the SI base unit of mass, defined since 2019 by fixing the Planck constant. Body weight, groceries, luggage allowances and most product weights outside the US are given in kilograms.
Worked example
Convert 150 lb: 150 × 0.45359237 = 68.0388555, so 150 pounds is 68.0388555 kilograms. Likewise 100 lb = 45.359237 kg.
Estimating in your head
Divide by 2.2 for a quick figure; it is off by about 0.2%. For 150 lb that gives 68.2 kg, against 68.0389 exactly.
Going the other way
To convert kilograms to pounds, divide by 0.45359237 (or multiply by 2.20462262185). The swap button between the boxes opens that page.
How this works
kg = lb × 0.45359237
1 lb = 0.45359237 kg and 1 kg = 1 kg, both by definition, so the factor is their ratio: 0.45359237 exactly. Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.
Frequently asked
How many kilograms are in a pound?
1 pound = 0.45359237 kilograms, exactly. The value follows from the unit definitions, so it never changes.
How do I convert pounds to kilograms?
Multiply by 0.45359237. For example, 100 lb × 0.45359237 = 45.359237 kg.
What is 1,000 lb in kilograms?
1,000 lb = 453.59237 kg. The table next to the converter lists more common values.
Is the result rounded?
Only on screen. The page computes with the exact definitions and removes floating-point noise past 15 significant digits; pick 3 to 12 significant figures, or use Copy result for the full value.
Sources
- NIST SP 811 Appendix B.8 — Factors for units listed alphabetically
- Federal Register 59-5442 (1959) — Refinement of values for the yard and the pound
- Wikipedia — Avoirdupois system
Reviewed Oct 17, 2026 · test vectors fixtures/units/mass/lbs-to-kg/