Via Current & Thermal Calculator

Vias carrying real current — power planes, high-current signal transitions — need the same IPC-2221 scrutiny as traces. This calculator rates a plated via barrel's current capacity and thermal rise from its drill size, plating thickness, and barrel length, applying the internal-layer derate IPC-2221 requires. Run it before committing to a via count on a power stitching pattern, or while diagnosing an unexpectedly hot via on a returned board.

Via Current & Thermal Rating

Plated barrel, IPC-2221 internal derate

Show your work

Finished hole Ø

Plating thickness

µm

Board thickness

Temp rise

°C

Via count

Current / via

0.95 A

Current × 1

0.95 A

Barrel area

39.56 mil²

Barrel R(dc)

1.08 mΩ

θ / via

162.8 K/W

θ × 1 parallel

162.8 K/W

Formula

A = \frac{π}{4} \cdot ({D_{out}}^{2} - D^{2})

D_{out} = D + 2 t

I = 0.024 \cdot {Δ T}^{0.44} \cdot A^{0.725}

θ = \frac{L}{k_{Cu} \cdot A}

R = \frac{ρ \cdot L}{A}

I_{total} = N \cdot I θ_{total} = \frac{θ}{N}

0.024, 0.44 and 0.725 are IPC-2221's curve-fit constants for internal layers; a via barrel always counts as internal.

D = finished hole diameter, inside the plating
t = plating thickness
L = board thickness (the barrel's length)
A = barrel cross-section, the plated ring only (mil²)
ΔT = allowed temperature rise (°C)
I = current per via (A)
θ = thermal resistance of one via (K/W)
k_Cu = 385 W/(m·K), copper's thermal conductivity
ρ = 1.72×10⁻⁸ Ω·m, copper's resistivity at 20 °C
N = number of vias in parallel

Thermal figure is conduction through the copper barrel only; unfilled vias carry no meaningful heat in the air column. For thermal pads, stitch 4–9 vias of 0.3 mm on a 1.0–1.2 mm pitch.