Via current rating.
How much current one plated via carries — and how many you need. Models the barrel as a conductor of circumference × plating thickness.
Barrel-ampacity estimate (IPC-2221 internal-conductor form applied to the plated wall, A = π·d·t). It ignores the via’s role as a thermal bottleneck and the copper it dumps into — for a power path, validate the full thermal model in TRM. See also the thermal via array tool.
The method
A plated through-hole is a hollow copper cylinder. Its current-carrying copper is the barrel wall — a conductor whose effective cross-section is the circumference times the plating thickness:
A = π · d · t (mil²)
d = finished hole diameter (mil)
t = copper plating thickness (mil)We then apply the IPC-2221 internal-conductor relation (vias are surrounded by board material, so the conservative internal constant applies):
I = k · ΔT^0.44 · A^0.725 , k = 0.024 (internal)N vias in parallel multiply the current — but only if they share the load evenly, which depends on the copper feeding them.
Reality check
- A single 0.3 mm / 1 mil-plated via at 10 °C rise carries roughly 0.9 A — the origin of the “≈1 A per via” rule of thumb.
- This is ampacity, not thermal sign-off. A via can be electrically fine yet still be the thermal choke point — that’s what the thermal via array tool and TRM address.
- Filled-and-plated or copper-filled vias carry far more; this model is for standard plated barrels.