Size a plated through-hole via for the current it has to carry. Enter the finished hole diameter, plating thickness and the temperature rise you allow, and get the current capacity per via plus the barrel copper cross-section, voltage drop and power loss. Based on the IPC-2221 conductor-sizing charts.
The board is cut through the via's axis. d is the finished hole diameter, t the copper plated on the barrel wall — the metal that carries the current — and L the via length, the finished board thickness.
Standard plated through-hole vias only. The barrel is treated as an IPC-2221 conductor of the same copper cross-section, using k = 0.048 — the usual assumption for a via, whose copper reaches both outer surfaces. Resistance uses copper resistivity at the barrel's operating temperature (ambient + rise) and ignores the annular rings and the connecting copper.
A calculator tells you one via is not enough — you still have to place the stitching, keep it on the right net, and redo it when the current or the stackup changes. In Flux, you just ask. Tell Flux how much current a net carries and it sizes the vias, stitches enough of them and keeps the copper consistent — live on the canvas.
Your 0.3 mm vias with 25 µm plating carry about 1.9 A each at a 10 °C rise, so for 2 A:
I've placed 2 stitching vias at the layer change on VBAT_5V. If you go to 0.2 mm vias I'll bump that to 3.
The IPC-2221 conductor-sizing formula applied to the via barrel, evaluated client-side as you type.
Unrolled, the plating is a tube of copper: the annulus between the finished hole of diameter d and the drilled hole around it, t thick. Area in mils².
The same IPC-2221 curve used for traces, solved for current instead of width, with k = 0.048. Divide your current by it and round up to get the number of vias.
The barrel is a conductor as long as the board is thick. Vias in parallel divide that resistance, and the voltage drop and power loss follow from your current.
