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Embedded Microstrip Impedance Calculator


Provide values for the four parameters H1, H, T, W, and the relative permittivity of the dielectric. Click the button corresponding to the characteristic impedance to calculate its value. ( 0.1< W/H < 3.0; 1 < εr < 15 )

Select the units for all dimensions: mm mils
H1 (Dielectric thickness) : blank space mm mils
H (Height above reference plane): blank space mm mils
T (Trace thickness): blank space mm mils
W (Trace width): blank space mm mils
εr (Relative permittivity): blank space
 (Characteristic impedance): blank space ohms
C0 (Capacitance): blank space pF/cm pF/inch
Tpd (Propagation delay time): blank space psec/cm psec/inch


  • The formulas used here are taken from the Design Guide for Electronic Packaging Utilizing High-Speed Techniques (4th Working Draft, IPC-2251, February 2001)
    Equations from IPC-2251
  • Range of valid parameters specified in the Design Guide: 0.1< W/H < 3.0; 1 < εr < 15
  • Note the equations used here are proposal currently being evaluated by IPC. The embedded microstrip impedance formula is an approximation and the results are highly sensitive to the values of the variables. The accuracy of the equations was observed to be slightly better for higher permittivities.
  • For typical PCB parameters (εr = 4, H1 = 61.37 mil, H = 30 mil and T = 1.37 mil), the deviation of the calculated results obtained using a 2D numerical field solver, is listed below:
    0.1 < W/H < 1.0 within 20%
    1.0 < W/H < 3.0 20%--40%
    0.1 < W/H < 1.0 within 5%
    1.0 < W/H < 2.2 within 20%
    2.2 < W/H < 3.0 20%--40%