Thermal Relief Spoke Current Calculator
Current capacity of a thermal-relief pad from spoke count, width and copper weight — IPC-2221 with the equivalent trace width.
Thermal reliefs trade current capacity for solderability — full (solid) connections wick heat away from the joint and cause tombstoning/cold joints on hand-soldered boards. For pads carrying more than a few amps, use solid connections on internal layers and reliefs only on the layer you solder, or increase spoke count/width.
Thermal Relief Spoke Calculator computes the current a thermal-relief pad can carry through its spokes — free, instant and private in your browser. Layout engineers balancing solderability against current on plane-connected pads use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About Thermal Relief Spoke Current Calculator
Thermal Relief Spoke Calculator computes the current a thermal-relief pad can carry through its spokes using the standard engineering relation: combined section A = n·w·t through IPC-2221's internal curve I = 0.024·ΔT^0.44·A^0.725. Worked live: four 0.3 mm spokes in 1 oz copper carry about 2.8 A at a 10 °C rise — fine for logic, marginal for power. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use Thermal Relief Spoke Current Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use Thermal Relief Spoke Current Calculator?
- ✓Implements the real formula — combined section A = n·w·t through IPC-2221's internal curve I = 0.024·ΔT^0.44·A^0.725 — with the substitution shown, not a black box
- ✓Built for layout engineers balancing solderability against current on plane-connected pads
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate thermal relief spoke?+
The current a thermal-relief pad can carry through its spokes follows combined section A = n·w·t through IPC-2221's internal curve I = 0.024·ΔT^0.44·A^0.725. For example, four 0.3 mm spokes in 1 oz copper carry about 2.8 A at a 10 °C rise — fine for logic, marginal for power. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
Should power pads use thermal reliefs or solid connections?+
Hand-soldered boards need reliefs or the plane wicks heat and the joint goes cold. For pads above a few amps, use solid connections on internal layers and a relief only on the layer you solder — or widen/multiply the spokes and verify with this calculator.
Why did my ground pin tombstone in reflow?+
One pad connected to a plane with full copper while the other had a relief: the solid side stayed cold longer, its solder wetted late, and surface tension on the hot side stood the part up. Matching thermals on both pads prevents it.
Is the Thermal Relief Spoke Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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