Skin depth calculator — copper & aluminium

About 8.5 mm. Skin depth is the depth at which current density falls to 1/e (about 37%) of its surface value, from δ = √(ρ / (π × f × μ₀ × μᵣ)) with μ₀ = 4π × 10⁻⁷ H/m and μᵣ = 1 for non-magnetic metals. At 50 Hz the copper figure is about 9.3 mm.

Skin depth grows with the square root of resistivity, and aluminium (ρ = 2.65 × 10⁻⁸ Ω·m) is more resistive than copper (ρ = 1.724 × 10⁻⁸ Ω·m), so aluminium skin depth runs about 1.24× deeper at the same frequency. Both metals are non-magnetic, so μᵣ = 1 for each.

Roughly 66 µm, and the quick-reference table on the page lists 1 MHz copper at 0.066 mm. Above about 1 MHz both copper and aluminium depths fall into the micrometre range, so plating thickness and surface finish matter more than conductor bulk — relevant for RF connectors and busbars.