Controlled Impedance Stackup Calculator

About this calculator

A microstrip trace — a copper trace running over a solid ground plane, separated by a dielectric layer of height H and relative permittivity Er — behaves as a transmission line whose characteristic impedance depends on trace width W, copper thickness T, and the dielectric properties of the board material. The IPC-2141 approximation gives the effective dielectric constant and Z0 ≈ (87/√(Er+1.41))·ln(5.98H/(0.8W+T)), along with a propagation delay derived from the effective permittivity.

Matching this impedance to a target — typically 50Ω single-ended or 90–100Ω differential — prevents signal reflections that cause data errors, EMI, and eye-diagram closure on high-speed interfaces. PCB designers and hardware engineers use this calculator early in stackup planning for USB, HDMI, Ethernet, and other controlled-impedance signals, then hand the resulting width/height targets to the fab house to confirm against their process capability.