Via current calculator
Current one plated via carries for a temperature rise, its resistance, and how many vias in parallel a target current needs.
- Vias for 5 A
- 3 1.67 A each, assuming equal sharing.
- Barrel cross-section
- 0.0255 mm²
- Resistance per via
- 1.14 mΩ
- Resistance of 3 in parallel
- 381 µΩ
- Voltage drop across the group
- 1.91 mV
- Power in the group
- 9.54 mW
| Finished hole | Barrel (mm²) | Current (A) | Resistance (mΩ) | Vias for 5 A |
|---|---|---|---|---|
| 0.15 mm (5.9 mil) | 0.0137 | 1.21 | 2.13 | 5 |
| 0.20 mm (7.9 mil) | 0.0177 | 1.46 | 1.65 | 4 |
| 0.25 mm (9.8 mil) | 0.0216 | 1.69 | 1.35 | 3 |
| 0.30 mm (11.8 mil) | 0.0255 | 1.90 | 1.14 | 3 |
| 0.35 mm (13.8 mil) | 0.0295 | 2.11 | 0.99 | 3 |
| 0.40 mm (15.7 mil) | 0.0334 | 2.31 | 0.88 | 3 |
| 0.50 mm (19.7 mil) | 0.0412 | 2.69 | 0.71 | 2 |
| 0.60 mm (23.6 mil) | 0.0491 | 3.06 | 0.60 | 2 |
| 0.80 mm (31.5 mil) | 0.0648 | 3.74 | 0.45 | 2 |
| 1.00 mm (39.4 mil) | 0.0805 | 4.37 | 0.36 | 2 |
How this is calculated
A = π/4 · ((d + 2p)² − d²) = π · (d + p) · p d finished hole, p plating I = 0.048 · ΔT^0.44 · A^0.725 A in mil², IPC-2221 external R = ρ20 · (1 + 0.00393 · (T − 20)) · L / A L board thickness N = ceil( I_target / I )
- Method
- IPC-2221 has no via chart. The common approximation treats the barrel as an external conductor of the same cross-section. It is generally conservative: the barrel is short and connects to pads and planes that carry heat away, which the long-trace curve does not credit.
- Plating
- Default 25 µm, the IPC-6012 Class 3 average hole-wall copper. Class 2 average is 20 µm. Thin-spot minimums are lower (18 µm Class 2, 20 µm Class 3), so a barrel can be locally thinner than the average.
- Valid range
- Temperature rise 10 to 100 °C and up to 35 A per conductor, as charted in IPC-2221. Equal current sharing between vias is assumed; vias far from the source carry less.
- Copper
- Resistivity 1.724 × 10⁻⁸ Ω·m at 20 °C (annealed copper, IACS), 0.00393 per °C, evaluated at ambient plus rise.
- IPC-2221B, Generic Standard on Printed Board DesignRevision B, 2012, section 6.2
- IPC-6012F hole-wall copper, average and thin point, by class (summary)JLCPCB, Understanding IPC-6012 Standards, accessed 13 October 2026
Questions
With 25 µm plating the barrel is 0.0255 mm², which the IPC-2221 external curve rates at 1.90 A for a 10 °C rise. With 20 µm (Class 2 average) it drops to about 1.6 A. A 5 A rail needs three of them at 25 µm, four at 20 µm, by this method.
The IPC-2221 curve describes a long conductor cooling into still air. A via is only as long as the board is thick, here 1.6 mm, and both ends land on copper that pulls heat out. Measured via temperature rise is usually lower than this predicts, so treat the count as a safe floor.
IPC-6012 requires an average hole-wall copper of 20 µm for Class 2 and 25 µm for Class 3. The calculator defaults to 25 µm. Most prototype fabs build to Class 2 unless you ask, so set 20 µm when the drawing does not call out Class 3.
Usually not for heat, sometimes for regulation. A 0.3 mm via through 1.6 mm of board is about 1.14 mΩ at 35 °C, so three in parallel carrying 5 A drop about 1.9 mV. On a low-voltage, high-current rail that adds to the plane and trace drop.