PCB Trace Resistance Calculator

Created by Álvaro Díez
Reviewed by Dominik Czernia, PhD and Jack Bowater
Last updated: Feb 02, 2023

We don't think we need to explain what the PCB trace resistance calculator does, but just in case - it calculates the resistance of traces in PCBs.

It also doubles as a PCB trace voltage drop calculator, as it uses Ohm's Law. Simply input the geometric parameters to receive your result. By default, this calculator acts as a PCB copper trace calculator, but you can adapt it to your material of choice.

PCB trace resistance equation - Ohm's law made practical

When it comes to calculating the resistance of a material, Ohm's Law should be the first thing that comes to mind. However, its basic form ($R = \frac{V}{I}$) is not always very useful. For example, if, during the design phase, we wanted to calculate the resistance of a wire that forms a PCB trace, it is not always possible to measure the voltage drop in the trace or the amperage that goes through it.

💡 If you can't measure the voltage drop, you may be able to find it anyway! Visit our voltage drop calculator to see how.

Those are the instances where we should use the PCB trace resistance calculator. Internally, this calculator solves the resistance equation for traces in a PCB substrate:

$R = \frac{\rho L}{TW} (1 + \alpha(T_{\text{amb}} - 25\degree\text{C})$

where,

• $R$ is the resistance;
• $L$ is the length of the trace;
• $T$ is the thickness of the trace;
• $W$ is the width of the trace; and
• $T_{\text{amb}}$ is the ambient temperature.

There are two constants in this equation, namely $\rho$ and $\alpha$, which are the resistivity and the resistivity temperature coefficient, respectively. By default, they are set to the values for copper, making this a PCB copper trace calculator.

If this equation seems intimidating, don't worry, the PCB trace resistance calculator will do all the work for you if you use it correctly.

How to use the PCB trace resistance calculator?

The PCB trace resistance calculator works in a straightforward way: fill in the Inputs, and you will get the Output. The main fields of the calculator are:

• Trace width, which you can obtain using our PCB trace width calculator;
• Trace length, or the distance from the beginning to the end of the trace;
• Trace thickness - it can be thought of as the "height" of the trace; and
• Ambient temperature, which is the temperature of the environment in which the PCB traces operate.

The PCB trace calculator also works in reverse, so as long as you input enough parameters, it will calculate the missing ones for you.

PCB trace voltage drop calculator - the hidden feature

Once you have the resistance of your PCB traces, it is very simple to use Ohm's Law to calculate the voltage and current that would flow through it. We want to make your life as easy as possible, so we have included a PCB trace voltage calculator of sorts that lets you do just that in the Advanced Mode.

Clicking on the Advanced Mode button will show three more fields that include the voltage drop of the PCB trace, the resistance (as calculated above), and the current. Fill in 2 of them, and you will get the third one instantly. Just remember to use our PCB trace current calculator to make sure you are within the specifications of your PCB substrate traces.

Two more fields will also appear in the Inputs section: the resistivity and the resistivity temperature coefficient. By default, they are set to the values of copper, but you can change them, turning this PCB copper trace calculator into a PCB trace calculator for any metal. More power to you!

Álvaro Díez
Inputs
Trace width (W)
mil
Length (L)
in
Trace thickness (T)
oz/ft²
Ambient temperature
°F
Output
Resistance
Ω
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