Convert Mil (mil) to Femtometer (fm) instantly.
About these units
Mil (mil)
A mil is an imperial-derived engineering unit equal to one-thousandth of an inch. It is used extensively in manufacturing, machining, and electrical engineering. Printed circuit board (PCB) trace widths, for instance, are often measured in mils because the unit provides a convenient scale for precision without resorting to decimals in inches. Because 1 mil equals 25.4 micrometers, it occupies a scale appropriate for tolerances in industrial production, coatings, film thickness, and gaskets. The mil is especially common in the United States, where certain engineering standards still rely on the imperial system. It provides an intuitive small-scale measurement for technicians accustomed to inches, helping avoid errors that might result from metric conversions.
Femtometer (fm)
A femtometer, equal to 10⁻¹⁵ meters, is the scale at which the structure of atomic nuclei becomes measurable. Also known historically as a "fermi," this unit is used extensively in nuclear physics to describe the radii of protons, neutrons, and nuclei, which typically span 1–10 femtometers. At this scale, the strong nuclear force dominates interactions, and classical intuition breaks down almost entirely—quantum mechanics provides the only meaningful framework. The femtometer also plays a role in high-energy particle experiments, where the wavelengths of probing particles (like high-velocity electrons) may be expressed in femtometer increments. These small wavelengths allow researchers to resolve sub-nuclear structures. While invisible to any optical instrument, distances in the femtometer range can be inferred through scattering experiments, such as those performed in particle accelerators.