Convert Femtometer to Micron

A femtometer is a metric unit of length equal to one quadrillionth of a meter (1×10⁻¹⁵ m). It is the standard unit for measuring sub-atomic dimensions, particularly the size of atomic nuclei. The femtometer is also known historically as the fermi.

The femtometer was defined using the SI prefix femto- (from Danish femten, meaning fifteen), adopted by the CGPM in 1964 to denote one quadrillionth. The synonymous name fermi was named after Italian physicist Enrico Fermi.

Femtometers are used to express the size of atomic nuclei (typically 1–10 fm in diameter), the range of strong nuclear forces, and characteristic dimensions in particle physics. The proton charge radius is approximately 0.84 fm.

SI prefix femto- adopted in 1964; the unit became standard in nuclear physics through the late 20th century. The name fermi (after Enrico Fermi) was used informally from the 1950s but officially superseded by femtometer.

A micron is a deprecated synonym for the micrometer (1×10⁻⁶ m). Although officially obsolete since 1967, the term remains in widespread informal use in microscopy, biology, materials science, and industrial filtration.

The term micron was coined in 1879 by the BIPM as a unit name for one millionth of a meter. It was officially deprecated in 1967 in favor of the SI-compliant name micrometer to avoid confusion with the device (also called a micrometer) used for precise mechanical measurement.

Microns are used informally in filtration ratings (e.g., a 5-micron water filter), industrial coatings, microscopy specifications, and pharmaceutical particle-size descriptions. The conversion to micrometers is exact: 1 micron = 1 µm = 1×10⁻⁶ m.

Introduced in 1879, deprecated by the BIPM in 1967, but retained in informal industrial and scientific usage well into the 21st century.