Trace Width Calculator
How wide does a trace need to be to carry a given current without overheating the board? This calculator works both directions with either IPC-2221's classic external and internal charts or the newer IPC-2152 method, which accounts for board thickness and nearby copper planes. Enter a current and copper weight to get the minimum trace width, or enter a width to find its current-carrying capacity. Useful the moment you're laying out power distribution, or checking a design against fab-house constraints before or after boards come back.
Trace Width
IPC-2221 or IPC-2152 — solve for required width or a trace's current capacity
Internal layers: k = 0.024, b = 0.44, c = 0.725
External layers: k = 0.048, b = 0.44, c = 0.725
- I = current (A)
- ΔT = allowed temperature rise (°C)
- A = cross-section (mil²)
- W = trace width (mil)
- t = copper weight (oz); 1 oz of copper is 1.378 mil thick
- k, b and c are curve-fit constants from IPC-2221's charts.
IPC-2221 is a conservative DC estimate for a bare trace in still air. Internal layers derate to roughly half the external current for the same geometry. Add margin for long runs, adjacent heat sources, and pulsed loads.
IPC-2221 vs IPC-2152
IPC-2221's trace-current charts go back to testing from the 1950s. They give one curve for external traces and, for internal traces, simply halve the current. Board thickness, board material and nearby copper planes aren't considered.
IPC-2152 (2009) replaced that data with new thermal testing. It found that internal traces run as cool as or cooler than external ones, and that a solid copper plane close to the trace can cut its temperature rise roughly in half. Its method starts from one baseline chart and adjusts it for copper weight, board thickness, board material and the distance to the nearest plane.
Use IPC-2152 when you know your stackup, especially on multilayer boards with planes, where it usually allows a narrower trace. Without a plane it can call for a wider trace than IPC-2221's external chart, because its testing showed that chart is only safe on boards larger than about 3 × 3 in with planes. IPC-2221 internal matches IPC-2152's own conservative chart, so it's the safe choice when you don't know the stackup, on small boards, or in vacuum.
IPC publishes these as charts, not equations. The IPC-2152 option uses published curve fits of the charts (Geoffrey Hunter's NinjaCalc fits and Jack Olson's board and plane factors) and applies the board adjustments as changes in temperature rise, the way IPC-2152's appendix reports them. Treat the result as an estimate within a few percent of the charts and leave margin.