PCB Trace Width Calculator

Calculates the minimum copper trace width an IPC-2221 PCB needs to carry a target current at a chosen temperature rise, or the maximum current a given trace width can carry. Handles internal and external layers, which dissipate heat differently, copper weights from 0.5 to 2 ounces, and an optional trace length to also estimate resistance, voltage drop, and power loss.

Pick a mode, layer, and copper weight, then type values as key=value tokens. For width-for-current, give a current such as current=3; for current-for-width, give a trace width such as width=20mil or width=0.5mm. Add temprise=10 to set the target temperature rise in degrees C, and length=0.1m or length=4ft to also see resistance, voltage drop, and power loss over that length.

Most online IPC-2221 calculators only run in one direction and hide the temperature rise assumption, the resistivity baseline, and how far short IPC-2221 falls of the newer IPC-2152 standard. This one computes both directions straight from the formula, includes a reference table across a current range, and your inputs never leave your device.

Why does an internal trace need to be wider than an external trace for the same current?

An internal trace is buried inside the board with no direct exposure to air, so it dissipates heat far less efficiently than a trace on the outer surface. IPC-2221 models this with a much smaller constant for internal traces, k = 0.0021 versus k = 0.0647 for external, which the formula turns into a wider required trace for the same current and temperature rise target.

Should I use IPC-2221 or IPC-2152 for my design?

IPC-2221 is the classic empirical formula and works fine for early estimates and low-risk designs. IPC-2152, published in 2009, also accounts for board thickness, trace location, and nearby traces, and generally recommends wider traces for the same current, so a high-current or safety-critical design should be cross checked against IPC-2152 charts or your fabricator's own capability data.

What temperature rise should I pick for my design?

10 degrees C is the most common default and a reasonable starting point for general purpose boards. A tighter rise like 5 degrees C is more conservative for temperature sensitive designs, while a looser rise like 20 degrees C or higher lets you use a narrower trace but runs the board hotter, so check your enclosure and nearby component ratings before choosing a high value.