femtometre

unit of measurement

Also known as: fm

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June 26, 2026

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A femtometer is a unit of length equal to 10⁻¹⁵ meters, meaning it is one quadrillionth of a meter. The prefix "femto-" signifies one quadrillionth (10⁻¹⁵) of a unit. Historically, the femtometer was also known as a fermi. This unit is extremely small, used to measure subatomic distances.123

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Atomic model
…measuring nuclear sizes is the femtometer (fm), which equals 10⁻¹⁵ meter. The diameter of a nucleus depends on the number of particles it contains and ranges from about 4 fm for a light nucleus such as carbon to 15 fm for a heavy nucleus such as lead. In spite of…
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…measuring nuclear sizes is the femtometer (fm), which equals 10⁻¹⁵ meter. The diameter of a nucleus depends on the number of particles it contains and ranges from about 4 fm for a light nucleus such as carbon to 15 fm for a heavy nucleus such as lead. In spite of…
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