Convert Pounds (lbs) to Kilograms (kg)

The formula

To convert pounds to kilograms, multiply the pound value by the exact conversion factor:

kg = lb × 0.45359237

• kg — the result in kilograms.
• lb — the input weight in avoirdupois pounds.
• 0.45359237 — the exact number of kilograms per pound, fixed by the 1959 International Yard and Pound Agreement.

The reverse formula is: lb = kg ÷ 0.45359237 = kg × 2.20462.

Worked example

Using the calculator’s default input of 160 lb:

1. Take the pound value: 160.
2. Multiply by 0.45359237: 160 × 0.45359237 = 72.575.

So 160 lb ≈ 72.58 kg.

Conversion table

Common pound values converted to kilograms:

Pounds (lb)	Kilograms (kg)
1	0.454
5	2.268
10	4.536
25	11.340
50	22.680
100	45.359
120	54.431
140	63.503
160	72.575
180	81.647
200	90.718
250	113.398
300	136.078

History & standards

The avoirdupois pound has roots in medieval trade across Britain and mainland Europe. The name comes from the Old French “avoir de pois” (goods of weight). It was standardised across the British Empire in 1844 and formally aligned with the metric system by the 1959 International Yard and Pound Agreement, which fixed 1 lb = 0.45359237 kg exactly — making it possible to convert perfectly between the imperial and metric systems.

The kilogram is the SI base unit of mass, introduced during the French Revolution. From 1889 to 2019 it was defined by the International Prototype Kilogram (IPK) — a platinum-iridium cylinder in Sèvres, France. Since 2019 the kilogram is defined by fixing the numerical value of the Planck constant, removing any dependence on a physical artefact.

Common applications

• Body weight and healthcare. US patients and physicians use pounds; the rest of the world uses kg. Converting is essential for medical records, BMI calculations and medication dosing.
• International shipping and e-commerce. US sellers ship in pounds; international carriers charge by kg. Accurate conversion prevents surcharges and underpaid postage.
• Gym and strength training. US barbells and plates are labelled in lb; Olympic and European equipment uses kg. Athletes need to convert to track true progress.
• Food import and export. USDA and FDA labelling requires both lb/oz and metric units on packaged goods sold in the US.
• Aviation and automotive. Aircraft maximum-takeoff-weight and vehicle payload are often stated in both lb (US FAA documentation) and kg (international aviation standards).

Reverse conversion

To convert kilograms back to pounds, divide by 0.45359237 (or multiply by 2.20462): lb = kg × 2.20462 — or use our kg to pounds calculator.

Limitations & gotchas

• Rounding. Using 0.454 instead of 0.45359237 introduces an error of about 0.09% — fine for body weight but not for precise pharmaceutical or engineering calculations.
• Troy pounds exist but are rarely used. A troy pound (373.24 g, 12 troy oz) differs from the avoirdupois pound (453.59 g) used here. The troy pound is almost never used in everyday commerce.
• Mass vs weight. The pound and kilogram are both units of mass. “Weight” in everyday language is used loosely to mean mass, which is correct in commerce but not in strict physics (where weight is force, measured in Newtons).
• US vs UK usage. Both countries use avoirdupois pounds (same definition), so 160 lb means the same weight on either side of the Atlantic.

Sources & references

• NIST SP 811 — Guide for the Use of the International System of Units (SI).
• BIPM — The International System of Units (SI), 9th edition (2019).
• 1959 International Yard and Pound Agreement (fixing 1 lb = 0.45359237 kg exactly).