Cable Impedance Calculator — Characteristic Impedance

Characteristic Impedance

Z0 = √(L / C)

where L is inductance per metre (H/m) and C is capacitance per metre (F/m).

Propagation Delay

Delay = √(L × C) in seconds per metre

Velocity Factor

The signal speed as a percentage of the speed of light, VF = 1 / (delay × c). Real screened audio and digital cables typically fall in the 60–80% range; if your L and C give a much lower figure, double-check the units (µH/m and pF/m).

Return Loss vs Target

Return loss (dB) = −20 × log₁₀|Γ|, where Γ = (Z0 − Z_target) / (Z0 + Z_target).

Return loss is reported as a positive figure: a larger value means a better impedance match (less reflected signal). A perfect match (Z0 = Z_target) gives infinite return loss, shown as “N/A”.