PCB Trace Current Capacity and Temperature Rise Calculator
This calculator answers the question every layout review asks: how much current can this trace carry before the board heats too much? It uses the IPC-2221 relationship between cross-sectional area, temperature rise and current.
Your numbers
Finished copper width of the trace.
Inner layers shed heat poorly, so IPC-2221 uses a smaller constant.
Rise above ambient, not absolute temperature.
Your results
IPC-2221 curves are an approximation for isolated traces. Planes, vias, nearby heat sources, airflow and board thickness change real temperature rise. Verify with a thermal test or the current IPC-2152 data for critical designs.
Maximum current vs trace width
Sweeps Trace width from 0.2 to 5, holding your other inputs fixed.
Review your power layout rules
Optional: get an expert review of how design rules flow into your ERP and engineering change process.
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How to use it
Enter the finished trace width and pick the copper weight from the stackup. Choose external or internal layer, then set the temperature rise you can tolerate above ambient. The maximum current appears instantly, and the chart shows how current capacity grows as the trace gets wider. Use the density output as a sanity check, because very high amps per square mm usually mean you should widen the trace or add copper pour.
The formula behind it
IPC-2221 gives I = k x dT^0.44 x A^0.725, where I is current in amps, dT is temperature rise in degrees C, and A is the cross-sectional area in square mil. The constant k is 0.048 for outer layers and 0.024 for inner layers. Area is width in mil times thickness in mil, and 1 oz copper is about 1.378 mil thick.
- Capacity is not linear in width: doubling area adds about 65% current
- Temperature rise has a weak 0.44 exponent
- Inner layers carry roughly half the current of outer layers
Reading the result
Worked example: a 1 mm trace in 1 oz copper on an outer layer with a 20 C rise carries about 3.2 A. Pick a rise that suits the product, since a 10 C rise is conservative for medical or aerospace boards, while consumer power boards often accept 30 C or more. Remember the board still has to survive reflow, rework and the maximum ambient of the end product.
Common mistakes
Using the wrong copper thickness after plating is common: outer layers start from a base foil that gains plating, so finished copper is heavier than the foil callout. Another mistake is ignoring neck-downs at pads and vias, which become the hottest points. Always check the narrowest section of a power path, not the typical width.
Frequently Asked Questions
Is IPC-2221 still the right reference?
IPC-2221 trace curves date from older testing. IPC-2152 is the newer current-carrying standard and accounts for board thickness and planes. IPC-2221 remains a common quick estimate and is usually conservative.
What temperature rise should I choose?
Many designers use 10 C to 20 C for reliable products and up to 30 C for cost-driven boards. Choose based on the maximum ambient, the laminate Tg and the lifetime requirement of your product.
Why are inner layers rated lower?
Inner traces are surrounded by dielectric, which conducts heat worse than air convection and radiation from the surface. The IPC-2221 constant for inner layers is half that for outer layers.
Does this cover vias?
No. Vias have their own current limits based on barrel plating thickness and diameter. Use several vias in parallel for power paths and verify the plating thickness with your fabricator.
If your PCBA drawings and BOM data live in an ERP, Netray can help route design rules and approvals into the engineering change flow.
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