Convert Femtometer (fm) to Megaparsec (Mpc) instantly.
About these units
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.
Megaparsec (Mpc)
A megaparsec is equal to one million parsecs, making it one of the principal units for describing intergalactic distances and the scale of the observable universe. Astronomers use Mpc to measure the distances between galaxies, galaxy groups, and galaxy clusters, as well as to express the scale of cosmic structures like the cosmic web. Megaparsecs are also central to cosmology because the Hubble constant — which describes the rate of cosmic expansion — is measured in units of kilometers per second per megaparsec. Thus, the Mpc sits at the heart of research on dark energy, large-scale structure formation, and the Big Bang. While hardly intuitive for everyday understanding, the megaparsec offers unmatched practicality for professional astronomy. It simplifies equations and visualization of the universe at the grandest scales.