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Microstrip Transmission Line Characteristic Impedance Calculator Using The IPC-2141 Formula

   The characteristic impedance (Zo) of a microstrip transmission line can be calculated using the active calculator or the formula at the bottom of the page.

[diagram of PCB layers]


Enter the εr of the PCB: 
Enter the width of the track:     mm    
Enter the thickness of the track:    mm  
Enter the thickness of the dielectric:   mm   Characteristic Impedance (Zo):    Ohms 

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The calculator gives very similar results to those in Table 1 of an article at 

The following formula is given in the above article by Polar Instruments.

[IPC2141 formula]

Where εr is the Relative Dielectric Constant

W is the Width of track

t is the Thickness of track (1 oz/ft2 = 0.035 mm)

h is the Thickness of dielectric


Note that the "h", for dielectric thickness in this formula is omitted in some other Polar publications.

 The original source of formula is IPC-2141: Controlled Impedance Circuit Boards and High-Speed Logic Design, April 1996. 

IPC have their website at:

This calculator is provided free by Chemandy Electronics in order to promote the FLEXI-BOX

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