Pounds to Kilograms

What this tool is used for

• Filling in a shipping form or an airline baggage allowance that is specified in kilograms.
• Converting a body weight for a medical form or a dosage table that assumes metric.
• Reading a US recipe or product spec into the units the rest of your equipment uses.
• Checking a freight quote where the carrier charges per kilogram.
• Converting a gym plate loading written in pounds to compare against a metric bar.

Frequently Asked Questions

What is the factor and a quick estimate?

Divide by 2.2046226218, or for mental arithmetic halve and subtract 10%: 150 lb → 75 − 7.5 = 67.5 kg (true 68.0). Good to within about 1% across ordinary body weights.

Which pound is this?

The international avoirdupois pound, 0.45359237 kg exactly. The troy pound (373.24 g, still used for precious metals) and the historical London and Tower pounds are different units — a real source of error when reading old documents.

How do I convert stones and pounds together?

Multiply stones by 14, add the remaining pounds, then convert the total. 11 st 4 lb is 158 lb, which is 71.67 kg. Converting the stones and pounds separately and adding the results is a frequent mistake.

Does this matter for medication dosing?

Very much — weight-based dosing is calculated in mg/kg, so an unconverted or mis-converted pound figure is a genuine clinical hazard. Clinical systems record kilograms specifically to remove this conversion step.

Why is the abbreviation lb?

From the Latin libra pondo, "a pound by weight" — lb comes from libra. The same root gives the UK's £ sign and the Italian lira.

Why is the conversion factor exact?

Because the pound has been defined as exactly 0.45359237 kg since the 1959 international agreement — it is a definition, not a measurement. That is why the digits terminate rather than running on.

How are body weights conventionally rounded?

To the nearest tenth of a kilogram in clinical settings and to the whole pound elsewhere. Converting 154 lb to 69.85312 kg reports precision the original never had — the input's own resolution should govern the output.

Common errors and gotchas

• Rounding to a whole kilogram on a dosage or a freight band, where the boundary is exactly what matters.
• Confusing pounds with pounds-force in an engineering context, where mass and force are different quantities.
• Using 2.2 as the factor. It is 2.20462, and the error compounds noticeably above a few hundred pounds.
• Mixing up stones and pounds when converting a UK body weight, which is quoted as both.
• Assuming a scale's displayed conversion is exact. Many round internally before showing the result.