PCB Trace Width Calculator
Minimum PCB trace width for a current (IPC-2221), with resistance.
About this tool
Enter the current, allowed temperature rise, copper weight and layer. The tool gives the minimum trace width in mm and mil, plus the trace's resistance, voltage drop and power loss over its length.
How trace width is calculated
The classic IPC-2221 design formula relates current to temperature rise and copper cross-section: I = k × ΔT^0.44 × A^0.725, where A is in square mils and k is 0.048 for external layers and 0.024 for internal layers, which are surrounded by insulating laminate and can't shed heat as easily. Rearranged for area, then divided by copper thickness (1 oz/ft² is about 35 µm or 1.378 mil), it gives width. A 1 A trace with a 10°C rise on 1 oz outer copper needs about 0.30 mm (12 mil); on an inner layer it needs about 0.78 mm. Doubling the copper weight halves the width. The tool also estimates resistance (copper at 20°C), voltage drop and power loss, so you can check long power traces. Honest limits: IPC-2221's curves are old and conservative; IPC-2152 accounts for board thickness and copper planes and often allows narrower traces. Vias, nearby planes, airflow and high ambient temperatures change the result, so leave margin. Not engineering advice. The wire gauge converter and the Ohm's law calculator are related.
Frequently asked questions
How wide should a PCB trace be for 1 amp?
About 0.3 mm (12 mil) on a 1 oz outer layer for a 10°C rise, or about 0.78 mm on an inner layer.
Why do inner layers need wider traces?
They're surrounded by laminate that conducts heat poorly, so IPC-2221 halves the k factor for internal traces.
What thickness is 1 oz copper?
About 35 µm (1.378 mil).
Is IPC-2221 still used?
Yes, but IPC-2152 is the newer, more accurate standard and often allows narrower traces.
Is my data sent anywhere?
No. Everything is calculated in your browser, and nothing is stored or sent.