How do you calculate Carrier Drift Velocity?

Use the formula vd = I / (n × A × q). Drift velocity is the average speed at which charge carriers move along a conductor when carrying current. Enter the values you know in the calculator above and it solves for the remaining variable.

What is the formula for Carrier Drift Velocity?

The Carrier Drift Velocity formula is vd = I / (n × A × q), where vd—Drift velocity (m/s); I—Current (A); n—Carrier density (1/m³); A—Conductor cross-sectional area (m²); q—Carrier charge (C).

Carrier Drift Velocity

vd = I / (n · A · q)

Calculator

Drift Velocity

Current

Carrier Density

Cross Section

Carrier Charge

Result

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Formula

vd = I / (n × A × q)

Description

Drift velocity is the average speed at which charge carriers move along a conductor when carrying current. It is surprisingly slow—often well under a millimetre per second—even though the electrical signal itself travels near the speed of light. The huge number of carriers makes a large current possible at this tiny drift speed.

Variables

vd — Drift velocity (m/s)
I — Current (A)
n — Carrier density (1/m³)
A — Conductor cross-sectional area (m²)
q — Carrier charge (C)

Practical Notes

In copper carrying a typical current density, vd is on the order of 0.1 mm/s. The current density J = n·q·vd ties drift velocity to ampacity and electromigration limits.

Related Concepts

All Fields & Electromagnetism formulas →

Coulomb’s Law Electric Field of a Point Charge Electric Potential of a Point Charge Gauss’s Law (Electric Flux) Lorentz Magnetic Force Force on a Current-Carrying Wire Force Between Parallel Wires Magnetic Field of a Straight Wire

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