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Classical electron radius: size, dimension and comparison

The adopted reference is about 2.8179 fm.

classical radius; not a measured size

fm means femtometer: a unit used to measure the nuclei of atoms. Imagine 1 millimeter split into one trillion equal pieces: one piece measures 1 fm.

A length derived from a classical model of the electron.

Explore at this scale
Classical electron radius, interpreted illustration
Interpreted illustration · dimension stated in the fact sheet.

What does this number measure?

A length derived from a classical model of the electron. This radius is a constant calculated from its charge and mass. It does not describe a little ball whose surface has been measured: no internal size of the electron is established here.

Compare the stated dimensions

The comparison uses the number in each fact sheet: altitude, height, diameter, length or distance, depending on the reference. Two values in metres do not necessarily describe the same property.

Compare with Helium nucleus in the explorer →

Source and limitations

Catalogue order of magnitude; a source is provided, but this measurement has not been individually audited.

Classical electron radius: a conceptual diagram, with the gold radial segment representing the theoretical radius. The sphere is a graphical convention; this radius is not a measured size of the electron.