1 pound = 0.4536 kilograms
Convert pounds to kilograms with an exact, internationally defined factor — 1 lb = 0.45359237 kg (exact).
pounds to kilograms
Computed with the exact factor · NIST SP 811
| Pound | Kilogram |
|---|---|
| 0.5 lb | 0.2268 kg |
| 1 lb | 0.4536 kg |
| 2 lb | 0.9072 kg |
| 3 lb | 1.361 kg |
| 5 lb | 2.268 kg |
| 10 lb | 4.536 kg |
| 25 lb | 11.34 kg |
| 50 lb | 22.68 kg |
| 100 lb | 45.36 kg |
Exact factor details
- Exact factor
- 1 lb = 0.4536 kg (exact definition)
- Significant digits
- up to 4 significant digits shown
- Data source
- NIST SP 811 — verified against official tables
Why lb to kg trips people up
Weight and mass conversions between kilograms, pounds, and ounces. The avoirdupois pound has been defined as exactly 0.45359237 kilograms since 1959, so these conversions are exact by international agreement. The avoirdupois pound is exactly 0.45359237 kilograms by international agreement. The kilogram is the SI base unit of mass, defined by the Planck constant since 2019.
In everyday use, pound and kilogram are compared directly, though the pound is technically a unit of mass in the avoirdupois system. For cooking, gym training, and shipping the distinction does not matter — the exact definition keeps every conversion consistent. Ounces and grams are linked through the same definition: one ounce is exactly 28.349523125 grams.
Use the quick-reference table for the amounts people actually look up, and the converter above for everything in between. Both are computed from the same factor at full precision, so the table and the converter can never disagree — there is no second, rounded copy of the data anywhere on this page.
Frequently asked questions
Is the lb to kg conversion exact?
Yes. 1 lb = 0.45359237 kg (exact) and SI base unit are exact definitions, so the conversion is exact — results are rounded only for readability.
How do I convert lb to kg in my head?
Divide pounds by 2.2 — 220 lb is about 100 kg.
Why do other sites show slightly different lb to kg results?
They round at different steps. This page computes with the full-precision factor and rounds only the final displayed number, so small trailing digits can differ from sites that round earlier.