What the PCB Via Current Calculator does
This calculator works out how much current a plated through-hole via can carry, how many you need for a net, and what the barrel's resistance costs you. It starts from the geometry - the copper in a plated barrel is an annulus, not a solid cylinder - and applies the IPC-2221 current equation to that cross-section, which is the usual industry approximation.
A 0.3 mm via with 25 um of plating has about 25,500 square micrometres of copper, roughly the same as a 29 mil track in 1 oz foil. That is the number worth carrying around: a via is a short piece of track standing on end.
How to use it
- Enter the finished drill diameter and the plating thickness. 25 um (1 mil) is the usual class 2 minimum; your fabricator will state their actual process figure.
- Enter the board thickness, which is the barrel length and therefore sets its resistance.
- Enter the current the net carries and the temperature rise you will allow.
- Read the current per via and the number needed. If you already know how many vias will fit, enter that to see the margin.
- Check the drill-size table to see whether a bigger via or more small ones is the better answer for your layout.
Reading the results
The figure is conservative in two directions at once. IPC-2221 itself is conservative, and a via is a much shorter thermal path to the planes than a track is - real barrels carry considerably more than this suggests.
Vias in a group never share current equally: the ones nearest the source take more, and the imbalance grows with the spacing. That is why designers fit more than the calculated minimum rather than exactly it.
Barrel resistance is usually negligible for volt drop - microhms - but it matters when a via group is also the thermal path, because the power dissipated there has to leave through the same copper.
Worked example: a 3 A rail crossing to an inner plane
A 0.3 mm drill with 25 um of plating has an outer diameter of 0.35 mm, so the copper annulus is pi/4 x (0.35^2 - 0.30^2) = 0.02553 mm2, which is 39.56 mil2.
Applying IPC-2221's external-layer equation to that area at a 10 C rise gives I = 0.048 x 10^0.44 x 39.56^0.725 = 1.90 A per via. Three amps therefore needs two vias, and most designers would fit three or four to allow for uneven sharing.
Through a 1.6 mm board the barrel's resistance is 1.724e-8 x 0.0016 / 2.553e-8 = 1.08 milliohms, so 1.5 A through one drops 1.6 mV. Negligible for regulation - but four such vias carrying 3 A between them dissipate only about 2.4 mW, which tells you the group is not a thermal problem either.
Formulas and scoring rules
- Barrel copper area
A = pi/4 x ((d + 2t)^2 - d^2)d is the drill diameter and t the plating thickness. The barrel is a tube, not a rod.- Current per via
I = k x dT^0.44 x A[mil^2]^0.725IPC-2221 with k = 0.048, applied to the barrel cross-section - the common industry approximation.- Vias needed
n = ceil(I(net) / I(per via))Then add margin, because vias do not share current equally.- Barrel resistance
R = rho x h / Ah is the board thickness; rho(copper) = 1.724e-8 ohm.m at 20 C.- Equivalent track width
w[mil] = A[mil^2] / 1.378The 1 oz track with the same copper cross-section.
Why this is not in a standard
IPC-2221 and IPC-2152 both give charts for tracks. Neither gives a via current rating, because a via's behaviour depends on the planes it connects, the thermal environment of the barrel and whether it is filled - none of which a single chart can capture. The universal workaround, used here, is to treat the barrel as a track of the same cross-section.
That approximation is conservative, which is why it survives. A via sits in a solid block of laminate with copper at both ends, so it conducts heat away far better than an isolated surface track does. Where the number matters - a high-current interconnect in a production design - the answer is thermal measurement or simulation, not a formula.
Placing a via group so it works
Current takes the shortest path, so the vias nearest the source carry more than the ones further away. Spreading a group along the direction of current flow makes the imbalance worse; arranging them across the flow, close to the pad, makes it better. The same applies to thermal vias under a package: the ones under the hottest part of the die do most of the work.
Two other practicalities: thermal relief spokes on a plane connection deliberately restrict current as well as heat, so power vias should connect solidly; and via-in-pad needs filling and capping, which changes both the cost and the thermal behaviour. Ask the fabricator what their process supports before drawing a hundred of them.
Limitations: what the result does not prove
- There is no standard for via current capacity. This applies a track equation to a barrel cross-section, which is the common approximation and not a published rating.
- It assumes uniform plating. Real plating thins in the middle of a high aspect-ratio barrel, and the aspect ratio your fabricator can hold is a process limit worth asking about.
- Current sharing between vias in a group is assumed equal for the capacity figure. It never is, which is why the result carries a warning rather than a precise count.
- This is indicative only and not a compliance statement. A qualified engineer must verify high-current and thermal via designs by analysis or measurement against the applicable standards.
Privacy: where your data goes
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Standards and sources
- IPC-2221 - Generic standard on printed board design - checked 19 Sep 2026
- IPC-2152 - Standard for determining current-carrying capacity - checked 19 Sep 2026
- IPC-6012 - Qualification and performance specification for rigid printed boards (plating thickness classes)
Frequently asked questions
How much current can a PCB via carry?
A 0.3 mm via with 25 um of plating carries about 1.9 A at a 10 C rise by the IPC-2221 approximation. Larger drills and thicker plating carry more, roughly in proportion to the copper area of the barrel. The figure is conservative: measured barrels usually do better.
How many vias do I need for 5 A?
With 0.3 mm vias at 25 um plating, three by the calculation - and most designers would fit four to six, because vias in a group do not share current equally and the extra ones cost nothing but board area.
Does via size or plating thickness matter more?
Both act through the copper area, which is approximately pi x d x t for thin plating - so they matter proportionally. In practice plating thickness is fixed by your fabricator's process and drill size is your variable, which makes drill size the lever you actually have.
What is the resistance of a via?
About 1 milliohm for a 0.3 mm via through a 1.6 mm board with 25 um of plating. It is almost always negligible for volt drop, and becomes interesting only when a large group is carrying both current and heat.
Are thermal vias the same as current-carrying vias?
The geometry is the same but the design goal is not. A thermal via moves heat into an inner or bottom plane, and filled or capped vias do that considerably better than open plated ones. A current via only has to carry current, and open vias are fine.
Is one large via better than several small ones?
For current, a single large via usually gives more copper than several small ones in the same area, and one connection instead of many. For heat spreading and for redundancy, several small ones distributed under the source are often better. Layout constraints usually decide.
Why is there no IPC standard for via current?
Because a via's capacity depends on what it connects to - the planes, the laminate and whether it is filled - far more than a track's does. IPC-2221 and IPC-2152 both stop at tracks, and the industry applies the track equation to the barrel cross-section, which is what this page does.
Do thermal relief spokes affect current capacity?
Yes, considerably. A thermal relief deliberately restricts the connection between a pad and a plane so that soldering is easier, and that restriction carries current as well as heat. Power and ground vias should have a solid plane connection, not a relief.
Last reviewed by the A2Z.Tools team against the sources listed above.
