PCB Trace Width & Current Capacity Calculator (IPC-2221)
Calculate the minimum copper trace width required to carry a specified current within an allowable temperature rise, per the IPC-2221 standard.
Design Parameters
A
°C
oz
Note: External traces dissipate heat into open air more efficiently than internal traces, so they can carry the same current at a narrower width.
Minimum Trace Width (IPC-2221)
Required Trace Width (mm)0.786mm
Required Trace Width (mils)30.94mils
Copper Cross-Section Area42.39mils²
Copper Thickness1.370mils
Engineering Tips
- Always add a safety margin of 1.5× to 2× over the theoretical minimum to account for PCB manufacturing tolerances and thermal derating.
- For standard FR-4, the operating temperature should stay below 85°C. Assuming a 25°C ambient, a ΔT of 10°C to 20°C is a common design target.
PCB Trace Current Capacity and the IPC-2221 Standard
IPC-2221 is the industry-standard design guide for printed circuit boards. When current flows through a copper trace, resistive heating (I²R loss) raises the temperature of the board. The IPC-2221 equations calculate the minimum trace width that keeps this temperature rise within a safe limit, preventing delamination or substrate degradation.
Understanding Copper Weight (oz)
PCB copper thickness is specified by weight per square foot in ounces (oz), and ordered from manufacturers accordingly.
- 0.5 oz (half-ounce): ~0.685 mils (17.4 μm). Used for low-power signal traces.
- 1 oz: ~1.37 mils (34.8 μm). Standard copper weight for outer layers of commercial multilayer PCBs.
- 2 oz: ~2.74 mils (69.6 μm). Suitable for motor driver outputs and high-current power paths.