Convert Mile (mi) to Femtometer (fm) instantly.
About these units
Mile (mi)
The mile, equal to 5,280 feet, is a legacy of a long history of measurement stretching back to Roman times. Its ancestor, the Roman "mille passus" (thousand paces), established a rough distance of 1,480 meters, which evolved through medieval and early modern Europe into various regional miles. The English statute mile was standardized in 1593 and survives today in the United States, the United Kingdom (for roadways), and a few other territories. Despite being a non-metric unit, the mile remains deeply embedded in cultural and infrastructural systems. Road networks in the US are laid out with mile markers; athletic events include the famed "one-mile run"; and many people intuitively judge driving distances in miles. Aviation and international travel sometimes reference statute miles, though nautical miles dominate in navigation. Its long history and familiarity keep the mile relevant even in a metric world.
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.