PCB Trace Width Calculator

IPC-2221 Trace Width Standard

The IPC-2221 generic standard for printed board design defines empirical formulas for calculating the minimum copper trace width required to carry a given current without exceeding a maximum temperature rise. The formula is:

Area (mils²) = (I / (k × ΔT^0.44))^(1/0.725)

Where I is the current in amperes, ΔT is the permissible temperature rise above ambient in °C, and k is a constant that differs between external layers (k = 0.048) and internal layers (k = 0.024). Internal layers require wider traces because heat dissipation is more restricted.

Copper Thickness

Copper thickness is specified in oz/ft² (ounces per square foot), the industry-standard unit. One ounce of copper spread over one square foot produces a thickness of approximately 34.8 μm (1.37 mil). Standard PCB specifications include 0.5 oz (17.4 μm), 1 oz (34.8 μm), and 2 oz (69.6 μm). The trace width calculation divides the required cross-sectional area by the copper thickness to yield the minimum width.

Design Guidelines

Always add a safety margin of 20–50% above the calculated minimum width when designing PCBs, particularly for power traces. A temperature rise of 10°C above ambient is considered conservative for most applications. Use 40°C for less critical signal traces. For high-current power supplies, motor drivers, and charging circuits, target 5°C or lower and use multiple parallel traces or copper pours where possible.