PCB Trace Width Calculator
Calculate required trace width based on IPC-2221.
What is PCB Trace Width?
PCB Trace Width determines how much current a copper track can handle before it overheats. Unlike a wire in free air, a PCB trace is a flat ribbon of copper glued to a fiberglass (FR-4) insulator. If the trace is too narrow for the current, it acts like a fuse—heating up, delaminating from the board, or burning out completely.
This calculator uses the industry-standard IPC-2221 formulas to determine the minimum required width to keep the temperature rise within safe limits.
The IPC-2221 Formula
The IPC-2221 standard (formerly IPC-D-275) provides a conservative estimate for trace width based on allowable temperature rise.
I = k × ΔT0.44 × A0.725
Where:
- I = Maximum Current (Amps)
- ΔT = Temperature Rise (°C)
- A = Cross-sectional Area (mils²)
- k = Derating constant (0.048 for External layers, 0.024 for Internal layers)
Internal layers handle less current (about 50% less) because the FR-4 substrate acts as a thermal blanket, trapping heat inside the board. External layers can dissipate heat into the air via convection.
Practical Applications
- Power Distribution: routing 5A or 10A rails from a voltage regulator to the load. These traces must be wide (often >100 mils) or polygon pours.
- Motor Drivers: High current spikes in H-bridges require careful trace width calculation to prevent voltage sag and heating.
- Safety Compliance: UL and CE standards often limit the maximum temperature rise of a device (e.g., plastic enclosure limits).
FAQ
What is "1 oz Copper"?
It is a measure of thickness based on weight. 1 oz copper means 1 ounce of copper rolled flat covers 1 square foot. This equals exactly 1.37 mils (35 µm) thick. It is the standard thickness for most PCBs.
Why choose Internal vs. External layers?
External layers cool better, allowing narrower traces for the same current. Internal layers are insulated, so they get hotter faster. However, internal layers are essential for complex routing (EMI shielding or signal density).
IPC-2221 vs IPC-2152?
IPC-2221 is an older standard (1950s data) but is simple and widely used. It is generally conservative (safe). IPC-2152 (released 2009) is physics-based and more accurate but much more complex. For most hobbyist and general commercial designs, IPC-2221 is perfectly adequate.