PCB Via Array Calculator
Current capacity, resistance and number of vias needed for a power connection.
What it does
A single via can only carry a limited current. This works out each via’s capacity from its drill size and plating, and how many you need in parallel for your current.
Where it's used
Connecting power planes on different layers, high-current connector pads and thermal paths under hot parts.
How to use it
- Enter the total current.
- Enter the drill diameter and plating thickness (your fab’s standard is often 20–25 µm).
- Enter the board thickness.
- Read the current per via and the number of vias needed.
The formula explained
- A
- copper area of the via barrel ring
- I
- safe current per via (IPC-2221 external formula)
- R
- ρ·h / A — resistance of one via
- h
- board thickness (via length)
Worked example
10 A through 0.4 mm vias in a 1.6 mm board.
Inputs:
- Total current: 10 A
- Drill (hole) diameter: 0.4 mm
- Plating thickness: 25 µm
- Board thickness (via length): 1.6 mm
- Allowed temperature rise: 10 °C
- Ambient temperature: 25 °C
The calculator gives:
- Vias required: 5
- Current per via (max): 2.11 A
- Barrel cross-section: 0.02945 mm²
Tips and common mistakes
- Spread vias across the current path — vias far from the flow carry little.
- Plating thickness matters more than drill size for current.
- Add a couple of spare vias for reliability.
Questions people ask
Why does plating thickness matter so much?
The current flows in the thin copper barrel, not the hole. Its cross-section is roughly π × drill diameter × plating thickness, so doubling the plating roughly doubles the current a via can carry.
What plating thickness should I assume?
IPC-6012 asks for an average of about 20 µm for Class 2 boards and 25 µm for Class 3. Ask your board maker what they actually plate if you are close to the limit.
Are vias also used to move heat?
Yes. Arrays of “thermal vias” under the pad of a power part such as a QFN regulator carry heat to inner and bottom copper. Filled or tented vias stop solder from wicking away through them.
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Enter your values to get the result with the formula, substituted values and an explanation of each step.