PCB Trace Width Calculator
Calculate the minimum trace width for a given current using the IPC-2221 standard.
What is PCB trace width calculation?
PCB trace width determines how much current a copper trace on a printed circuit board can safely carry. An undersized trace acts like a fuse — it heats up and can burn through the board, damaging components and creating fire hazards. This calculator uses the IPC-2221 standard formulas to determine the minimum trace width for a given current, copper weight, and acceptable temperature rise.
The key factors are current (amps), copper thickness (typically 1 oz/ft2 = 35 um for standard PCBs), acceptable temperature rise above ambient, and whether the trace is on an internal or external layer. External traces dissipate heat more efficiently into the surrounding air, so they can be narrower than internal traces for the same current.
IPC-2221 standard
The IPC-2221 standard provides empirically-derived formulas for PCB trace sizing. The formula first calculates the required cross-sectional area in square mils, then converts to trace width based on copper thickness. External layers can handle about 44% more current than internal layers for the same geometry due to better thermal dissipation.
How to use this tool
Enter the maximum current the trace must carry, the copper weight (1 oz is standard), the maximum allowed temperature rise (10C is a common conservative choice), and whether the trace is on an internal or external layer. The calculator shows the minimum trace width in both mils and millimeters.
PCB design tips
- Always add a safety margin — use wider traces than the calculated minimum, especially for power traces.
- Use copper pours (ground planes) for high-current paths instead of narrow traces.
- Consider via stitching to connect copper on multiple layers for very high current paths.
- Signal traces can be much thinner (6-8 mil is typical) since they carry minimal current.
Frequently asked questions
What is copper weight and how does it affect trace width?
Copper weight refers to the thickness of the copper layer, measured in ounces per square foot. 1 oz copper is approximately 35 micrometers thick and is the most common for standard PCBs. Heavier copper (2 oz = 70 um) allows narrower traces for the same current because there is more cross-sectional area. Some power electronics PCBs use 3-4 oz copper.
Is the IPC-2221 formula accurate?
The IPC-2221 formulas are conservative estimates based on empirical testing from the 1950s-70s. Real-world performance varies with board material, ambient temperature, airflow, and nearby heat sources. The formulas provide a safe baseline — actual temperature rise is usually less than predicted. For safety-critical applications, thermal simulation or physical testing is recommended.