Electron Drift Velocity Calculator

How it works

I = n·A·e·v_d → v_d = I ÷ (n·A·e); J = I/A; E = ρ·J; μ = v_d ÷ E

The electrons that carry a current shuffle along astonishingly slowly — a fraction of a millimetre per second in household wiring — because copper has so many free electrons (one per atom, 8.5 × 10²⁸ per cubic metre) that a tiny average drift moves a large charge. The light comes on instantly because the electric field propagates along the wire at a good fraction of light speed and sets every electron moving at once, like water in an already-full hose.

Worked example

10 A in AWG 12 copper (3.3 mm²): J = 3 A/mm², v_d = 3 × 10⁶ ÷ (8.5 × 10²⁸ × 1.6 × 10⁻¹⁹) = 0.22 mm/s — about 75 minutes per metre.

Frequently asked questions