Convert Angstrom (Å) to Femtometer (fm) instantly.
About these units
Angstrom (Å)
The ångström, equal to 10⁻¹⁰ meters, is traditionally used to measure atomic scales, bond lengths, and wavelengths of electromagnetic radiation, particularly in the X-ray and ultraviolet regions. Although not an SI unit, the ångström persists because it aligns conveniently with many natural atomic dimensions — hydrogen's typical bond lengths, for example, are close to 1 Å. Scientists in crystallography, astronomy, materials science, and spectroscopy routinely use ångströms when describing the spacing between atoms in a crystal lattice or the wavelength of certain spectral lines. The convenience comes from avoiding unwieldy decimals: instead of writing 0.154 nm, one may write 1.54 Å. While modern research increasingly prefers SI nanometers or picometers, the ångström remains deeply embedded in scientific traditions and continues to serve as a practical shorthand for atomic-scale measurements.
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.