Milliardstel

Milliardstel is a German term for a fractional quantity equal to one part in a milliard. A milliard equals 1,000,000,000 (10^9) in the German long-scale naming, so a milliardstel is 1/1,000,000,000, i.e., 10^-9. In decimal form, this is 0.000000001. The word combines milliarde with the ordinal suffix -stel, indicating a subdivision of the whole.

It is used to express very small proportions, probabilities, or concentrations in science, engineering, and statistics. For example, 1 milliardstel of a liter is 1×10^-9 L, which is one nanoliter; 1 milliardstel per gram would be a concentration of about 1 ng/g if the density is near 1 g/mL. It also appears in error analysis and measurements where tiny fractions are significant.

In English, the closest equivalents are "one in a billion" or "one part per billion." The German term reflects the long-scale naming for the denominator 10^9, whereas English rarely uses a native compound form for such fractions.