Sierra Circuits’ free Impedance Calculator will help PCB designers calculate their trace widths, single-ended or differential impedances – for both microstrip and stripline models – and other parameters such as the dielectric height, the dielectric constant, and the trace thickness. The tool will also provide a guide for dielectric constant values for various PCB materials.

Here is a guideline to use our Impedance Calculator:

The first thing to do is to choose what kind of impedance you want: single-ended or differential.

How to calculate single-ended impedance:

Choose the dielectric constant based on the materials listed in the box below, choose the dielectric height based on your stack up. Enter the SE impedance you want, the trace width, and the trace thickness (if not already pre-filled), and click the “Calculate Impedance” or “Calculate Trace” buttons. If you want a specific trace width, you can adjust the dielectric height and the trace thickness until you achieve your desired trace width. Make sure that the impedance does not vary too much when you change the above values.

How to calculate differential impedance:

Enter the differential impedance you want, the trace width, the dielectric height, the dielectric constant, and the trace thickness, and click the “Calculate Trace” button to get the accurate trace width. If you want a specific trace width and separation, you can play around with different values in the calculator until you achieve it. Make sure that the impedance does not vary too much, it can be +/- 2%.

Note that, in both cases, Sierra’s Stackup team does not check the odd mode impedance, the even mode impedance, the propagation delay, the inductance, or the capacitance because most boards only require one or two types of impedance: single-ended and differential.

**LEARN MORE ABOUT CONTROLLED IMPEDANCE**

You can also read our HDI Stack-up Planner Tutorial!