Guide

Weights in everyday life: kilograms, pounds and ounces

Mass figures appear when shopping, in recipes, on parcels and in sports and engineering data. The metric system counts in grams, the Anglo-American one in pounds and ounces — and the German word Pfund does not mean the same as the English pound.

The base unit is the gram

The kilogram is the SI base unit of mass and the gram is one thousandth of it. Every other unit in the family relates to the gram through a fixed factor: one pound is 453.59237 grams, one ounce 28.349523125 grams, one tonne 1,000,000 grams. The factors are defined exactly, not rounded.

Pfund is not pound

In German usage “ein Pfund” usually means 500 grams, while the Anglo-American pound is exactly 453.59237 grams. The two values differ by about 10 %. German recipes mean 500 g, recipes from Britain or the United States mean 453.59237 g. The gram figure is unambiguous in both cases and therefore the safer reference.

Ounce, stone and carat

One pound has 16 ounces. In British everyday use the stone is the unit for body weight and equals 14 pounds, about 6.35 kilograms. The carat, by contrast, is not an everyday mass unit but a unit for gemstones: 1 carat is 200 milligrams, that is 0.2 grams. Carat as a mass and carat as the purity of gold are two different things sharing one name.

Rounding and measurement precision

The factors are exact, the measurements are not. A kitchen scale with a 1-gram display cannot resolve 0.001 g, and a bathroom scale shows one or two decimals at most. If a conversion returns many decimal places, round to the precision of the original measurement rather than to the precision of the factor.

Matching conversions

Matching tables

Unit family: Mass

Sources