Enter Material and Frequency
Formula
δ = √[2 / (ω µ σ)]
Here ω = 2πf, µ = µ0µr, and σ is conductivity in siemens per meter. The listed metals assume relative permeability µr = 1.
Worked Example
At 1 MHz, copper has a skin depth of about 0.065 mm, or 65 µm. Most current is concentrated near the surface rather than using the full conductor cross-section.
Skin depth decreases as frequency, conductivity, or magnetic permeability increases.
Assumptions and Limits
The formula assumes a good, uniform conductor and sinusoidal steady-state current. Conductivity changes with temperature and alloy composition.
Actual AC resistance also depends on conductor geometry, surface roughness, plating thickness, proximity effect, and nearby conductors.