PCB Trace Maximum Current Calculator (IPC-2221)

PCB Trace Current Capacity

Copper traces heat up when they carry current. IPC-2221 provides a widely used estimate of how much current a trace can handle for a chosen temperature rise. External layers dissipate heat better than internal layers, so they allow more current for the same geometry.

IPC-2221 Current Formula

$$I = k \times \Delta T^{0.44} \times A^{0.725}$$

$I$ is current in amperes, $\Delta T$ is allowed temperature rise in °C, and $A$ is cross-sectional area in square mils ($A = \text{width} \times \text{thickness}$). Use $k = 0.048$ for external layers and $k = 0.024$ for internal layers.

Copper Weight and Thickness

One ounce copper is about 1.378 mil thick. Two ounce copper is twice that. Wider traces and thicker copper both increase current capacity.

Frequently Asked Questions

What temperature rise is reasonable?

Many designers use 10 °C to 20 °C for signal traces. Power paths may allow more if the board and enclosure can tolerate the heat.

Why do internal traces carry less current?

Heat from inner layers must pass through laminate and adjacent copper before reaching air, so the same trace runs hotter for the same current.

Does trace length affect current capacity?

IPC current capacity depends on cross-section and temperature rise, not length. Length does affect resistance, voltage drop, and power loss.

Are IPC results exact limits?

They are conservative guidelines. Real boards depend on copper density, airflow, adjacent copper pours, and continuous load versus pulses.

What units does this calculator use for width?

Trace width is entered in mils (0.001 inch). Copper weight selects thickness in ounces, which is converted to mils internally.

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PCB Trace Current Calculator

PCB Trace Current Capacity

IPC-2221 Current Formula

Copper Weight and Thickness

Frequently Asked Questions

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