Size your copper for current in seconds. Pick external or internal copper, enter your current, allowed temperature rise and copper thickness, and get the minimum trace width plus cross-section, resistance, voltage drop and power loss. Based on the IPC-2221 conductor-sizing charts.
IPC-2221 sizes copper for current-carrying capacity only. Add margin for vias, connectors and thermal hotspots, and check the resistance and voltage drop before you commit — resistance uses copper resistivity at the trace's operating temperature (ambient + rise).
A calculator is a sanity check — but you still have to copy the number into a constraint dialog for every net, on every layer, and redo it when the copper weight changes. In Flux, you just ask. Tell Flux Copilot how much current a net carries and it sizes the copper, sets the net class and routes it — live on the canvas.
For 3 A on 1 oz external copper with a 10 °C rise, IPC-2221 needs:
I've set the VBAT_5V net class to 1.4 mm and routed it on the top layer. If it has to drop to an inner layer I'll widen it to 3.6 mm.
The IPC-2221 conductor-sizing formula, evaluated client-side as you type.
Area in mils². The constant k is 0.048 for external conductors and 0.024 for internal ones, because buried copper cannot shed heat into the air.
One ounce of copper per square foot is about 35 µm (1.378 mil) thick. Enter a thickness directly if your fab quotes microns or mils.
Divide the area by the thickness to get the width. Resistance, voltage drop and power loss then follow from the trace length and copper resistivity at ambient + rise.
