How to Create Your Own PCB Trace Width Calculator with Python

We all know the importance of traces in a PCB, but do we have a certain set of rules to make perfect designs? Of course, everything is listed in IPC guidelines. Let's talk about traces in more detail, like their length, width, current-carrying capacity, and type of parasitics that they consist of in a PCB design. We all know PCB traces are made of copper, a thin layer 1 or 2 OZ deep overall. Made of copper does not simply mean it does not have any resistance associated with it. The simple rule of resistance says, the thicker and wider the trace lower the resistance, and if the trace is thin and long, it has a lot of resistance. Does anybody want a signal power loss due to the trace.

Let's start with an example: if I am designing a power PCB and my trace is 10mm long and consists of a current of 5 A, then what will be the thickness? So we have to calculate by going into IPC, but in the era of computers, hand calculations are not done! Oh yes, you can use any online calculator, but why rely on them? We will design our independent code

Coming back to the main question - How wide should my copper trace be? The answer depends on several factors, like the current it must carry, the acceptable temperature rise, the copper thickness, and whether the trace is on an internal or external layer. To streamline this process, I developed a Trace Width Calculator in Python based on IPC-2152 guidelines. In this post, I’ll walk you through the design process, the parameters considered, and the features of the tool. And finally, how you can run it in any online Python compiler.

Parameters to Consider

When designing this calculator, I included key parameters that influence trace width:

1. Current Capacity (A) – The amount of current the trace must safely carry.

2. Temperature Rise (°C) – How much the trace temperature is allowed to increase above ambient.

3. Layer Type – External traces dissipate heat better than internal traces, so their formulas differ.

4. Copper Weight (oz/ft²) – Commonly 1 oz or 2 oz copper; affects thickness and resistance.

5. Trace Length (mm) – Important for calculating resistance and voltage drop.

6. Trace Width (mm) – Used when calculating maximum current from a given size.

Features of the Python Trace Width Calculator

The code is very lightweight, hence it does not have any UI. So it can be run online using any Python compiler. Here’s what my calculator can do:

Two Modes:
1)  Width from Current – Enter current, get the required trace width.
2) Current from Width – Enter width, get the maximum supported current.

Additional Calculations:

• Trace resistance (Ω)
• Voltage drop (V) for a given load
• Power loss in the trace (W)

How to Run the Trace Calculator in an Online Python Compiler

You don't need a local Python setup to use this tool. Just copy the code below given code and here is how to run the guide:

1. Visit any online Python compiler and paste the code into it. I am using Programiz just for example, you can choose any local one.

2. Click Run.

3. Follow the prompts in the terminal window to input your parameters.

First, it will ask the user to select between the two given modes: Width from Current or Current from Width. The respective output and prompts are given below:

Width from Current:

Current from Width:

This makes it possible to run the calculator from any device, even without installing Python.

Python Code:

import math
def calculate_trace_width(current, temp_rise=10, is_external=True):
    # IPC-2152 constants
    if is_external:
        k = 0.048
        b = 0.44
        c = 0.725
    else:
        k = 0.024
        b = 0.44
        c = 0.725

    width_mils = (current / (k * (temp_rise ** b))) ** (1 / c)
    width_mm = width_mils * 0.0254
    return width_mm

def calculate_trace_properties(width_mm, length_mm, copper_oz):
    # Constants
    copper_thickness_mm = {1: 0.035, 2: 0.07}  # in mm
    resistivity = 1.68e-8  # Ohm-meter for copper

    # Get thickness
    thickness_mm = copper_thickness_mm.get(copper_oz, 0.035)
    cross_section_mm2 = width_mm * thickness_mm

    # Convert to meters
    length_m = length_mm / 1000
    area_m2 = cross_section_mm2 * 1e-6

    # Resistance
    resistance = resistivity * length_m / area_m2
    return resistance

# --- Main Program ---

mode = input("Choose mode (1 = Width from Current, 2 = Current from Width): ")

if mode == '1':
    current = float(input("Enter current (A): "))
    temp_rise = float(input("Enter temperature rise (°C, default 10): ") or 10)
    layer = input("Is it external layer? (y/n): ").lower() == 'y'
    length_mm = float(input("Enter trace length (mm): "))
    copper_oz = int(input("Copper weight (1 or 2 oz): "))

    width_mm = calculate_trace_width(current, temp_rise, layer)
    resistance = calculate_trace_properties(width_mm, length_mm, copper_oz)
    voltage_drop = current * resistance
    power_loss = current ** 2 * resistance

    print(f"\n--- Results ---")
    print(f"Required trace width: {width_mm:.3f} mm")
    print(f"Trace resistance: {resistance:.4f} Ω")
    print(f"Voltage drop: {voltage_drop:.4f} V")
    print(f"Power loss: {power_loss*1000:.2f} mW")

elif mode == '2':
    width_mm = float(input("Enter trace width (mm): "))
    temp_rise = float(input("Enter temperature rise (°C, default 10): ") or 10)
    layer = input("Is it external layer? (y/n): ").lower() == 'y'
    length_mm = float(input("Enter trace length (mm): "))
    copper_oz = int(input("Copper weight (1 or 2 oz): "))

    width_mils = width_mm / 0.0254
    if layer:
        k = 0.048
    else:
        k = 0.024
    b = 0.44
    c = 0.725

    current = k * (temp_rise ** b) * (width_mils ** c)
    resistance = calculate_trace_properties(width_mm, length_mm, copper_oz)
    voltage_drop = current * resistance
    power_loss = current ** 2 * resistance

    print(f"\n--- Results ---")
    print(f"Maximum supported current: {current:.2f} A")
    print(f"Trace resistance: {resistance:.4f} Ω")
    print(f"Voltage drop: {voltage_drop:.4f} V")
    print(f"Power loss: {power_loss*1000:.2f} mW")

else:
    print("Invalid option.")

Final Thoughts:

Yet it is a very basic coding exercise, but to make it work, a designer needs to have proper parameter information and needs to go through the IPC guidelines for the trace calculator. The results may differ from the online calculators because some of them are running a previous version of the code. It is a simple project that can be deployed to any online Python compiler. If you have a proper Python compiler installed with all the packages, then a GUI can be deployed by extending the same code. Share the code and tag JLCPCB, and we will definitely consider giving a shoutout!