Tools / PCB via current calculator
PCB via current calculator
How much current a plated via can carry, how many you need in parallel and what each one adds in resistance, heat and inductance. IPC-2221 and IPC-2152 side by side.
Enter your hole size, plating and board thickness. Results update as you type, and the most conservative result is tagged.
IPC-2221 Internal curve
Most conservative
Maximum current
–
- Vias needed
- Voltage drop
- Power loss
- Via temperature
Treats the barrel like an inner-layer trace, wrapped in laminate. The conservative choice for most vias.
IPC-2221 External curve
Most conservative
Maximum current
–
- Vias needed
- Voltage drop
- Power loss
- Via temperature
Treats the barrel like an outer-layer trace cooled by air. Optimistic for a barrel buried in the board.
IPC-2152 Universal chart
Most conservative
Maximum current
–
- Vias needed
- Voltage drop
- Power loss
- Via temperature
Same copper area on the IPC-2152 chart. Planes and pours tied to the via lower the rise.
Each via
- Barrel cross-section
- Drill size
- Resistance
- Thermal resistance
- Inductance
- Aspect ratio
How the calculator works
A plated via is a copper tube. Its current rating comes from the copper area of that tube, run through the same IPC curves used for traces.
A via and a trace with the same copper cross-section get the same rating. The calculator works out the barrel area from the hole size and plating, then applies each model.
Barrel area
A = π × t × (d + t)
d is the finished hole diameter and t the plating thickness. The drill is d + 2t, which is also what sets the aspect ratio.
Current capacity
I = k × ΔT0.44 × A0.725
IPC-2221 uses k = 0.024 for its internal curve and 0.048 for its external curve. The IPC-2152 result uses the same universal-chart fit as our trace width calculator. A barrel buried in laminate behaves more like an inner-layer conductor, so the internal curve is the cautious choice.
Resistance and heat
R = ρ × L / A × (1 + 0.00393 × (T − 20 °C))
θ = L / (kCu × A)
ρ = 1.72 × 10−8 Ω·m, L is the via length (the board thickness for a through hole), T is ambient plus the rise, and kCu = 385 W/m·K. θ is the thermal resistance of one barrel from one side of the board to the other.
Inductance
L ≈ 5.08 × h × [ln(4h / d) + 1] nH
From Johnson and Graham, with h the via length and d the barrel outside diameter, both in inches. It covers the barrel alone; pads, antipads and the return path change the real value.
These are estimates for a single, isolated via. Real vias share heat with planes, pads and their neighbors, and a tight cluster runs hotter than one via on its own. Use the numbers to size via counts early, and confirm high-current paths thermally.
Via current for common hole sizes
Maximum current per via with 1 mil (25 µm) of plating in a 62 mil (1.6 mm) board at a 10 °C rise. Resistance is at 35 °C.
| Finished hole | Drill | IPC-2221 internal | IPC-2221 external | IPC-2152 | Resistance |
|---|---|---|---|---|---|
| 8 mil (0.20 mm) | 10 mil | 0.75 A | 1.49 A | 1.39 A | 1.57 mΩ |
| 10 mil (0.25 mm) | 12 mil | 0.86 A | 1.72 A | 1.56 A | 1.29 mΩ |
| 12 mil (0.30 mm) | 14 mil | 0.97 A | 1.95 A | 1.71 A | 1.09 mΩ |
| 16 mil (0.41 mm) | 18 mil | 1.18 A | 2.36 A | 1.98 A | 0.83 mΩ |
| 20 mil (0.51 mm) | 22 mil | 1.38 A | 2.76 A | 2.22 A | 0.67 mΩ |
| 30 mil (0.76 mm) | 32 mil | 1.83 A | 3.66 A | 2.75 A | 0.46 mΩ |
| 40 mil (1.02 mm) | 42 mil | 2.24 A | 4.48 A | 3.21 A | 0.35 mΩ |
Two small vias carry more than one via of twice the diameter: two 10 mil vias are rated about 1.7 A on the internal curve, one 20 mil via about 1.4 A.
Common questions
Which result should I use for vias?
Without other data, use the result tagged Most conservative, which is usually the IPC-2221 internal curve. Vias that join solid planes or large pours at both ends run cooler, so the IPC-2152 and external results are reasonable there.
How many vias do I need for a power connection?
Enter the current and the calculator divides it by the per-via rating and rounds up. Then add a few more: vias in a tight cluster heat each other, and one poorly plated via pushes its share of current through the rest. Extra vias are cheap insurance.
Does a bigger hole help?
Yes, but slowly. Current capacity follows the copper area of the barrel, which grows only in proportion to the diameter. Two small vias usually carry more than one large one, and, spaced apart, they nearly halve the inductance as well.
What plating thickness should I enter?
The thickness your fabricator will guarantee in the hole. About 1 mil (25 µm) is common, and IPC Class 3 builds call for more plating than Class 2. Thin plating is a common reason a via runs hotter than expected.
How do I size thermal vias under a part?
Use the thermal resistance figure. One 10 mil via through a 62 mil board conducts heat at about 180 °C/W, so ten in parallel come to about 18 °C/W. Filled or plugged vias conduct a little better and keep solder from wicking away from the pad.
Why does aspect ratio matter?
Plating has to reach the middle of the hole. Many fabricators quote 8:1 to 10:1 board thickness to drill as standard for through holes. Beyond that, plating thins in the middle and the price goes up. The calculator flags anything above 10:1.
Can Evertech review my power layout?
Yes. Via arrays, copper weight and current paths are part of every PCB layout and DFM review we do, and our production team builds the boards here in Cedarburg. Send your files for a quote.
Routing high current through layer changes?
Our engineers size power paths, via arrays and copper weights alongside our own production team in Cedarburg, Wisconsin. Send your files and we will take a look.