tenmillionth

Tenmillionth is the fraction 1/10,000,000. In scientific notation it is 1 × 10^-7, and in decimal form it is 0.0000001. It represents one part in ten million and is the reciprocal of ten million.

As a magnitude, a ten-millionth describes a very small portion of a whole or a correspondingly small measurement. For example, a length of 1 × 10^-7 meters equals 0.1 micrometers, and a time interval of 1 × 10^-7 seconds equals 100 nanoseconds. In concentration terms, it relates to the idea of parts per ten million, where 1 × 10^-7 corresponds to 0.1 ppm (parts per million).

There is no official SI prefix for 10^-7. The prefixes closest in magnitude are micro (10^-6) and nano (10^-9). Consequently, ten-millionth is typically described descriptively rather than as a standardized unit with a dedicated prefix.

Etymology and usage notes: the term arises from dividing a whole into ten million equal parts. It appears in mathematical, statistical, and technical contexts as a descriptive descriptor to express very small fractions or tolerances, rather than as a formal, universally standardized unit.

See also: parts per million, parts per ten million, decimal fractions.