Step-by-step walkthrough
Use this companion guide beside the interactive calculator to make sure you understand the “why” behind every click. Each section includes the classroom explanation, student-friendly language, and quick practice prompts.
Collect the data points listed below and double-check their units. Keeping an organized “givens” list is one of the fastest ways to reduce math errors and impress exam graders.
Step 1
Enter the maximum current the trace will actually carry, not just the nominal or average current.
Step 2
Pick a temperature rise you're comfortable with — 10°C is a common conservative default; 20-30°C is more aggressive.
Step 3
Choose copper weight (1 oz/ft² is standard for most consumer boards) and whether the trace sits on an outer or inner layer.
Treat it as a floor, not a target. Manufacturing tolerances, nearby heat sources, and long-term reliability all favor adding margin — many designers round up to the next standard width or add 20-30% headroom for anything carrying meaningful current.
External traces can shed heat directly into the air (and often get help from solder mask being thin); internal traces are sandwiched in fiberglass substrate, which is a much worse conductor of heat, so they need more copper cross-section to stay at the same temperature.
