Skin Depth Calculator (Skin Effect)

What this tool does

Alternating current does not use the whole wire: the eddy currents it induces push it towards the surface, and the current density drops by a factor of e for every skin depth. In copper that depth is about 9 mm at 50 Hz but only about 0.2 mm at 100 kHz and 6.5 µm at 100 MHz, which is why switch-mode transformers use litz wire and radio conductors are often silver-plated tubes. A magnetic material shrinks it much further, so steel has a far smaller skin depth than copper despite its higher resistivity. The resistance ratio treats the current as filling a ring one skin depth thick — a good estimate once the wire is several skin depths across.

Formula

δ = √(ρ ÷ (π f μ₀ μᵣ))

Variables

Worked example

Limitations

• The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
• The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.