1. a unit of length equal to one quadrillionth of a meter (10⁻¹⁵ m), used in nuclear and particle physics
Usage: physics; named after physicist Enrico Fermi
2. a type of estimation problem or thought experiment that involves making rough calculations with limited information
Usage: informal; also called a Fermi problem or Fermi question

Examples

• The nucleus of an atom has a radius on the order of a few fermi.
• In physics class, we solved a fermi about how many piano tuners work in Chicago.
• Particle physicists measure subatomic distances in fermi.
• A fermi is an extremely small unit of measurement used in nuclear research.
• The Fermi problem teaches students to break down complex questions into manageable estimates.