Microstrip Max Current Calculator

A calculator for solving the maximum current a microstrip can handle.






A microstrip is a flat conductor separated by an insulating dielectric from a large conducting ground plane and is mostly manufactured from a printed circuit board. It is similar in function to capacitors and inductors but only for very high frequencies. As such, microstrips are also subject to maximum ratings like capacitor and inductor. This calculator is designed to compute the maximum current that a microstrip can handle. The required entries are trace width, thickness, ambient temperature, temperature rise, and the microstrip length. 


$$I_{max} = \sqrt{ \frac{\Delta T}{215.3W^{-1.15} T^{-1.0}}}$$

$$R = \frac{\rho_{cu} L}{A} (1+\alpha_{cu} \Delta T)$$

$$V = I_{max} R$$

$$P = V I_{max}$$


$$\Delta T$$ = temperature rise

$$W$$ = trace width

$$T$$ = trace thickness

$$L$$ = trace length

$$\rho_{cu}$$ = resistivity of Copper = 1.7 x 10-6

$$\alpha_{cu}$$ = temperature coefficient of Copper = 3.9 x 10-3

*The maximum current formula is derived through curve fitting data found on IPC-2221


A microstrip can serve several purposes in microwave frequency circuits. They were invented because the required circuit inductance and capacitance values at very high frequencies are too small for standard inductors and capacitors. Like their lower-frequency counterparts, microstrips are also subject to maximum ratings. Microstrips are similarly used as capacitors and inductors as well as tuned circuits, filters, phase shifters. 

Further Reading

Textbook - Conductor Ampacity

Textbook - Copper Wire Ampacity Cable: Conductor and Insulator Tables

Worksheet - Wire Type and Sizes

  • S
    SoreEyes February 20, 2020

    There seems to be a problem with the calculator, Imax does not seem to change regardless of the input. Or am I missing something.

    Like. Reply
  • TDG March 15, 2022

    yes, the calculator is broken.  Nothing on the input side changes the current output.

    Like. Reply