Via Current Capacity (IPC-2221)

I = k × ΔT^0.44 × A^0.725

Quick answer

This calculator solves I = k × ΔT^0.44 × A^0.725 for I. With Constant k 0.5, Temperature Rise (°C) 50 °C, Barrel Cross-Section (mil²) 1000 mil², the result is 418.3 A.

Calculator

Result
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Formula

I = k × ΔT^0.44 × A^0.725

Description

The same IPC-2221 empirical formula applies to via barrels, where A is the cross-sectional area of the copper plating in the via barrel (not the via drill area). The via barrel is a hollow cylinder of plated copper, so A = π × d × t, where d is the drill diameter and t is the plating thickness (typically 0.7-1.0 mil for standard plating). A single standard via can typically handle 0.5-1A depending on temperature rise and plating thickness. For higher currents, use multiple vias in parallel.

Variables

  • I — Maximum current (A)
  • k — Constant (0.048 for external, use same as outer trace)
  • ΔT — Allowable temperature rise (°C)
  • A — Via barrel cross-section area (mil²)

Practical Notes

Via barrel area for a 12 mil drill with 1 mil plating: A = π × 12 × 1 ≈ 37.7 mil². Multiple vias in parallel share current; use 3-5 vias per amp as a conservative rule of thumb. Via-in-pad designs improve thermal performance but require filled and capped vias for surface mount components. Thermal vias under power components should be arrayed in a grid pattern.

Symbols and units

Symbol Meaning Default unit Accepted units
k Constant k — —
dT Temperature Rise (°C) °C °C
A Barrel Cross-Section (mil²) mil² mil²

Step by step

  1. 1. What you know: Constant k 0.5, Temperature Rise (°C) 50 °C, Barrel Cross-Section (mil²) 1000 mil²
  2. 2. The relation: I = k × ΔT^0.44 × A^0.725
  3. 3. Substitute: k = 0.5, dT = 50 °C, A = 1000 mil²
  4. 4. Result: I = 418.3 A

Worked examples

Minimum range

Given: Constant k 0.025, Temperature Rise (°C) 2.5 °C, Barrel Cross-Section (mil²) 10 mil²

Result: I = 0.1986 A

Low range

Given: Constant k 0.25, Temperature Rise (°C) 25 °C, Barrel Cross-Section (mil²) 100 mil²

Result: I = 29.04 A

Typical

Given: Constant k 0.5, Temperature Rise (°C) 50 °C, Barrel Cross-Section (mil²) 1000 mil²

Result: I = 418.3 A

High range

Given: Constant k 0.8, Temperature Rise (°C) 85 °C, Barrel Cross-Section (mil²) 10000 mil²

Result: I = 4488 A

Maximum range

Given: Constant k 8, Temperature Rise (°C) 850 °C, Barrel Cross-Section (mil²) 100000 mil²

Result: I = 656200 A

How I changes with Constant k

Constant k (input) I (result)
0.05 41.83 A
0.125 104.6 A
0.25 209.2 A
0.375 313.7 A
0.5 418.3 A
0.75 627.5 A
1 836.7 A
2 1673 A
3.5 2928 A
5 4183 A

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Frequently asked questions

How do you calculate Via Current Capacity (IPC-2221)?

Use I = k × ΔT^0.44 × A^0.725. With Constant k 0.5, Temperature Rise (°C) 50 °C, Barrel Cross-Section (mil²) 1000 mil², I works out to 418.3 A.

What is the formula for Via Current Capacity (IPC-2221)?

The formula is I = k × ΔT^0.44 × A^0.725. The same IPC-2221 empirical formula applies to via barrels, where A is the cross-sectional area of the copper plating in the via barrel (not the via drill area).

Related Concepts

All PCB & Traces formulas →
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