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Convert Pounds to Kilograms – Weight Converter

This converter converts a single numeric weight in pounds (lb) to kilograms (kg) using the internationally agreed fixed relationship between the avoirdupois pound and the kilogram. It is intended for general-purpose use such as fitness tracking, shipping estimates, and everyday unit conversion.

Results are produced using the exact international definition of the pound in terms of the kilogram and are suitable for informational and documentation purposes. For regulated or safety-critical contexts (for example clinical dosing, legal weights, or calibrated mass measurements), use calibrated instruments and follow traceability and accreditation requirements described in the references below.

Updated Nov 16, 2025

Interactive Converter

Convert between pound and kilogram with precision rounding.

Quick reference table

PoundKilogram
1 lb0.4536 kg
5 lb2.268 kg
10 lb4.5359 kg
25 lb11.3398 kg
50 lb22.6796 kg
100 lb45.3592 kg

Methodology

The converter uses a single fixed multiplication factor that links the avoirdupois pound to the SI base unit kilogram. This is a deterministic, lossless arithmetic conversion before rounding.

Displayed results are formatted to a reasonable number of decimal places by default but may be rounded to fewer digits depending on context; rounding and display do not change the underlying exact relationship.

Numerical representation follows standard floating-point arithmetic practices; small rounding differences may appear when showing many decimal places. For high-accuracy applications, follow instrument calibration and measurement uncertainty procedures in ISO/IEC 17025 and traceability guidance from national metrology institutes.

Worked examples

150 lb = 150 × 0.45359237 = 68.0388555 kg → typically shown as 68.04 kg (rounded to 2 dp).

0.5 lb = 0.5 × 0.45359237 = 0.226796185 kg → typically shown as 0.2268 kg (rounded to 4 dp for small masses).

200 lb = 90.718474 kg → typically shown as 90.72 kg (rounded to 2 dp).

Further resources

Expert Q&A

Is the conversion factor exact?

Yes. The international avoirdupois pound has been defined to equal exactly 0.45359237 kilograms. The multiplier used by this tool is exact by definition; displayed values are rounded for readability.

Why do I sometimes see different rounded results?

Different displays use different rounding rules and numbers of decimal places. The underlying conversion is exact; variations come from formatting (how many decimal places are shown) and floating-point representation when many decimals are requested.

Can I use results from this converter for medical dosing or regulated reporting?

This converter provides informational unit conversion only. For medical dosing, patient weight must be measured on a calibrated, traceable scale and documented per local clinical protocols. Calibration and measurement uncertainty must comply with applicable standards and facility procedures.

What does 'traceable' and 'calibrated' mean for weight measurements?

Traceability means the scale's calibration can be linked to national measurement standards through an unbroken chain of calibrations. Calibration and testing laboratories commonly follow ISO/IEC 17025. Always verify calibration certificates and intervals for regulated use.

Do you support stones and pounds input?

This converter accepts a single pounds value as input. If you have stones and pounds, convert the stones to pounds (1 stone = 14 pounds) then use this tool or use a combined converter that accepts stones and pounds.

How many decimal places should I use?

Choose decimals based on context: 1–2 decimals for shipping and fitness, 2–4 decimals for small masses or lab use, and follow institutional requirements for clinical or scientific reporting. Always document the rounding rule and consider measurement uncertainty where relevant.

Sources & citations