How do I convert pounds to kilograms?

kg = lb × 0.453592. Example: 150 lb × 0.453592 = 68.04 kg. 1 lb = 0.453592 kg (exact). Quick estimate: divide lb by 2.2. Used in aviation, medicine and cooking.

Lbs to Kg Formula: The Simple Math Behind Weight Conversion

Converting pounds to kilograms is one of the most common unit-conversion tasks. The math is simple — one multiplication — but the right formula plus a couple of mental shortcuts lets you do it without a calculator.

The exact lbs to kg formula

kg = lbs × 0.45359237. The constant 0.45359237 is the internationally defined exact conversion between the avoirdupois pound and the kilogram, ratified in 1959.

The fast mental shortcut

Divide by 2.2 (or more precisely 2.2046). 100 lbs ÷ 2.2 ≈ 45.5 kg — accurate to within 1% of the exact answer (45.36 kg). Good enough for gym plates, luggage and groceries.

Worked example: 150 lbs to kg

Exact: 150 × 0.45359237 = 68.04 kg. Shortcut: 150 ÷ 2.2 = 68.18 kg. Both round to ~68 kg.

Worked example: 200 lbs to kg

Exact: 200 × 0.45359237 = 90.72 kg. Shortcut: 200 ÷ 2.2 = 90.9 kg.

Reverse: kg to lbs formula

lbs = kg × 2.20462. Or mental shortcut: kg × 2 + 10%. 80 kg × 2 = 160 + 16 = 176 lbs (exact: 176.4).

Quick reference table

1 lb = 0.45 kg · 5 lb = 2.27 kg · 10 lb = 4.54 kg · 25 lb = 11.34 kg · 50 lb = 22.68 kg · 100 lb = 45.36 kg · 150 lb = 68.04 kg · 200 lb = 90.72 kg · 250 lb = 113.4 kg · 500 lb = 226.8 kg.

Common use cases

Bodyweight tracking, gym plate math (a 45 lb plate ≈ 20.4 kg), airline baggage allowances (50 lb = 22.7 kg), and US-to-metric recipe scaling.

Pitfalls to avoid

Don't confuse pounds-mass (lb) with pounds-force (lbf) — same number, different physics. And don't use 2.2 for medical doses; use the exact factor 2.20462 or the converter directly.

How this guide is researched and fact-checked

This article is produced by the ToolKit Pro Measurement Desk using ai-assisted research with human editorial verification against primary sources, and is checked by a human editor at the ToolKit Pro editorial desk before publication. Every number, formula and threshold quoted here is traced back to a primary standards body or health authority rather than to another blog, and each figure is re-computed with our own calculators so the worked examples and the live tools on this site always agree. When a definition changes — as with the 2019 SI redefinitions — the affected articles are re-checked and the “updated” date above is bumped.

Produced by: ToolKit Pro Measurement Desk — Unit conversion & measurement standards
Method: AI-assisted research, human-verified against primary sources
Reviewed by: ToolKit Pro editorial desk (human review)
Last reviewed: 2026-08-19
Corrections: spotted an error? Tell us and we will fix and re-date the page.

Sources & further reading

BIPM — The International System of Units (SI Brochure)
NIST — Guide for the Use of the International System of Units
WHO — Body weight & health guidance

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