IPC-2221 is the generic standard for printed board design. It contains an empirical equation that relates current, temperature rise and copper cross-sectional area. This calculator solves that equation for trace width (or for current), then uses the copper thickness you choose to convert between area and width.

Internal traces are surrounded by laminate and cannot shed heat to the air as easily. IPC-2221 therefore uses a constant of 0.024 for internal layers versus 0.048 for external layers, which makes an internal trace roughly 2.6 times larger in cross-section for the same current and temperature rise.

A 10°C rise is a common, conservative default for general designs. 20–30°C is often acceptable when the board has thermal margin. Use a smaller rise for precision analog circuits, high ambient temperatures or products with long life requirements.

For a given current, the required cross-sectional area is fixed, so doubling the copper thickness halves the width. Standard weights are 0.5 oz (about 17 µm), 1 oz (about 35 µm), 2 oz (about 70 µm) and 3 oz (about 105 µm) per square foot.

Not in the IPC-2221 heating equation. Length does set the resistance, voltage drop and power loss, so a long trace carrying high current may need to be wider than the thermal result to keep the voltage drop acceptable.

IPC-2221 is based on older empirical charts and is generally conservative, especially for internal layers. The newer IPC-2152 standard accounts for board thickness, nearby copper planes and airflow. Treat this result as a solid starting point, and verify high-current or safety-critical designs with testing or thermal simulation.

No. The calculator assumes a steady DC current in a straight trace. Vias, short current pulses, skin effect at high frequency and controlled-impedance lines need separate calculations.