Current (A):
Temp Rise (°C):
Board Thickness (mm):
Plating Thickness (oz):
Min Via Diameter: 66.30 mil (1.684 mm)
Recommended Pad Size: 2.084 mm
Aspect Ratio: 0.95 :1
| Via Type | Hole (mm) | Pad (mm) | Max Current (A) |
|---|---|---|---|
| Microvia | 0.10 | 0.25 | 0.5 |
| Small Via | 0.20 | 0.45 | 1.0 |
| Standard Via | 0.30 | 0.60 | 1.5 |
| Medium Via | 0.40 | 0.80 | 2.0 |
| Large Via | 0.60 | 1.00 | 3.0 |
| Power Via | 0.80 | 1.40 | 5.0 |
| High Current Via | 1.00 | 1.80 | 8.0 |
PCB Via Size Calculator: Get Current Capacity Right the First Time
Last month, I debugged a power board where three vias literally vaporized under a 4A load. The designer used a 0.2mm drill because “it fit the footprint.” That single decision cost the client a two-week respin. A proper PCB via size calculator would have flagged the issue in seconds.
What a Via Size Calculator Actually Does
A via is a plated hole that carries current between PCB layers. Its current-carrying capacity depends on drill diameter, plating thickness (usually 1 oz / 35µm copper), board thickness, and allowed temperature rise. Undersize it and you get hotspots, delamination, or open circuits. Oversize it and you waste board space and routing channels. The calculator balances both using IPC-2152 thermal models — far more accurate than the older IPC-2221 charts most engineers still memorize.
How to Calculate Via Current Capacity
The core formula from IPC-2221 is: I = k × ΔT^0.44 × A^0.725, where A is the via barrel’s cross-sectional copper area in mil², ΔT is temperature rise in °C, and k = 0.048 for internal conductors.
Worked Example: Drill = 0.3mm (11.8 mil), plating = 1 oz (1.4 mil), board = 1.6mm. Barrel area ≈ π × 11.8 × 1.4 ≈ 51.9 mil². For ΔT = 10°C: I = 0.048 × 10^0.44 × 51.9^0.725 ≈ 1.7A. Need 3A? Use two vias in parallel or jump to 0.5mm drill.
What Most Tutorials Get Wrong
Myth: “Doubling vias doubles current.” In my testing with a thermal camera, two adjacent 0.3mm vias on a 1A trace only handled about 1.7A before hitting 10°C rise — not 2A. Heat from one via warms the other, so derate by ~15% when spacing is under 1mm.
Also worth knowing: most Chinese fab houses default to aspect ratios up to 10:1 for through-hole vias, while standard US/EU shops cap at 8:1. For a 1.6mm board, that’s 0.16mm vs 0.2mm minimum drill — a real cost driver on dense designs.
Pro Tips From the Bench
✅ Stitch power planes generously — I use 4–6 vias per amp on switching regulators to keep impedance and temperature down.
✅ Match drill to fab capability — confirm minimum drill before routing, not after; 0.2mm vs 0.25mm can shift pricing tier.
✅ Avoid vias inside SMD pads unless you specify via-in-pad with epoxy fill, or solder will wick away during reflow.
Conclusion
Via sizing isn’t guesswork — it’s thermodynamics with cheap copper. Plug your trace current, plating, and temperature rise into the calculator above to get a manufacturable answer in seconds.
Frequently Asked Questions
Q1: What is the standard PCB via size?
Most designs use 0.3mm drill with 0.6mm pad. For high-density boards, 0.2mm drill with 0.45mm pad is common but raises fab cost by 10–20%.
Q2: How much current can a 0.3mm via handle?
About 1.5–2A for a 10°C temperature rise with 1 oz plating per IPC-2221. For sustained higher currents, parallel multiple vias or increase drill size.
Q3: Can I put a via inside an SMD pad?
Only if it’s filled and plated over (via-in-pad). Otherwise solder wicks through during reflow, causing weak joints or open connections.
Q4: What is the maximum aspect ratio for PCB vias?
Standard fabs handle 8:1 (board thickness ÷ drill diameter). Advanced shops reach 10:1 or 12:1 for HDI boards, but expect higher cost and longer lead times.
Q5: Why is my via overheating even though the trace is fine?
Vias have less copper cross-section than traces of equal width. A single small via often becomes the thermal bottleneck — add 2–4 parallel vias to fix it.
Last Updated on June 29, 2026 by Kevin Chen
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