Lbs to Kg Calculator

Background.

Since 1 July 1959 the pound has been defined as a fixed fraction of the kilogram: exactly 0.45359237 kg. Before that, countries using the pound kept slightly different standards of their own, and the international agreement on the yard and the pound settled them on one value. Every pounds-to-kilograms conversion is therefore a single multiplication with no measurement uncertainty in it.

The conversion turns up wherever American habits meet metric records: a barbell loaded in pounds in a US gym and logged against a kilogram programme, a bathroom-scale reading entered on a medical form, a parcel weighed at home for an international shipping label, a birth weight announced as 7 lb 8 oz. For a 225 lb barbell, a 45 lb bar with two 45 lb plates on each side, the answer is 102.0583 kg.

The pounds you enter are also split into whole pounds and leftover ounces, at 16 ounces to the pound. That exposes an easy mistake, typing 11.8 for a reading of 11 lb 8 oz, before the wrong figure is converted.

What is lbs to kg calculator?

Both units measure mass. The pound here is the avoirdupois pound used for body weight, food, freight and gym equipment in the United States, and still informally in the United Kingdom; the kilogram is the SI unit used nearly everywhere else. One avoirdupois pound is exactly 0.45359237 kilograms by definition, so one kilogram is about 2.2046 pounds. A pound divides into 16 ounces, which is why a decimal pound such as 11.5 lb reads as 11 lb 8 oz on a kitchen or baby scale.

How to use this calculator.

1. 01Enter the weight in pounds, anywhere from 0 to 2,000 lb. Decimals are fine.
2. 02If your reading is in pounds and ounces, divide the ounces by 16 and add them on: 7 lb 8 oz is 7.5 lb, 11 lb 4 oz is 11.25 lb.
3. 03Read the kilograms, then glance at the whole-pounds and ounces split to confirm the pounds figure is the one you meant.

The formula.

Kilograms = pounds × 0.45359237. The factor is exact by definition, so the only rounding anywhere is in how many decimal places you choose to keep. The split re-expresses your input rather than the result: whole pounds is the input rounded down to an integer, and the leftover ounces are the fractional part × 16. For 11.5 lb that is 11 lb and 0.5 × 16 = 8 oz. The reverse factor, 1 ÷ 0.45359237 ≈ 2.2046 pounds per kilogram, is where the familiar rule of thumb of dividing by 2.2 comes from.

A worked example.

Frequently asked questions.

References& sources.

1. [1]National Bureau of Standards (1959). Refinement of Values for the Yard and the Pound — establishes the international avoirdupois pound as exactly 0.45359237 kilograms, effective 1 July 1959.
2. [2]National Institute of Standards and Technology (2008). NIST Special Publication 811: Guide for the Use of the International System of Units (SI), Appendix B — Conversion Factors.