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SESK: Stuff Everyone Should Know · sesk.info/eng-electron-drift-velocity

In typical household copper wiring, how fast do electrons drift compared with the electrical signal?

Very slowly, typically a fraction of a millimeter per second; the signal travels much faster.

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  1. Near the speed of light
  2. About the speed of sound
  3. Slower than a snail, a fraction of a millimeter per second ✔

Why: The wire is already packed with free electrons. Pushing on one end shoves them all at once, like water in a full hose, so the light turns on instantly even though each electron barely moves.

Huh, didn't know that: In OpenStax's 12-gauge, 20-amp example, the signal travels about a trillion times faster than electron drift.

The dad joke
Electrons in a wire are like my kids on a Saturday. Lots of energy, barely moving.
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References

Answer: Slower than a snail, a fraction of a millimeter per second. The wire is already packed with free electrons. Pushing on one end shoves them all at once, like water in a full hose, so the light turns on instantly even though each electron barely moves.

  1. OpenStax University Physics Vol. 2, 9.2 Model of Conduction in Metals openstax.org/books/university-physics-volume-2/pages/9-2-model-of-conduction-in-metals
    Drift velocity is quite small, since there are so many free charges.
    Checked 2026-10-10.

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