Calculator for Trace Width of Differential Pairs

As soon as you need to design a PCB with controlled impedance tracks you'll need to calculate the correct trace width for your application.
In order to find the right trace width you can enter your PCB manufacturer's layer stack-up (or choose one from the presets), the required impedance, allowed impedance tolerance and spacing between the two differential traces.
Please note that all trace width calculations are only approximations since the physics behind it are pretty complicated and exceed the capabilities of practically every calculator. For this reason you'll always need to define an allowed impedance tolerance and choose a trace width within that margin based on what works best in your specific use case.

A Differential Pair consists of two traces on one of the two outer layers that couples through the dielectric with a ground reference plane.


Trace Width for Differential Pairs (Edge-Coupled Surface Microstrips)

Differential impedance (Zd)
Ω (≥ 70 and ≤ 140)
Tolerance for Differential impedance
% (≥ 0 and ≤ 50)
Trace spacing (s)

Values ≥ 4 and ≤ 8 mils are generally recommended.

mil
mm


Differential Impedance from Trace Width:
Formula Differential Impedance from Trace Width for Differential Pairs
Trace Width from Differential Impedance:
Formula Trace Width from Differential Impedance for Differential Pairs