Current Capacity Calculator
IPC-2221 power-law model
Determine the maximum safe current for your PCB traces. Input your trace width and copper weight to calculate the current capacity with specified temperature rise.
Quick answer
A 10 mil (0.254 mm) trace on 1 oz copper carries about 0.9 A on an external layer and about 0.4 A on an internal layer for a 10 °C temperature rise, using the IPC-2221 power law.
Worked example (10 mil, 1 oz, 10 °C rise, 50 mm long)
| External layer capacity | 0.89 A |
|---|---|
| Internal layer capacity | 0.44 A |
| Resistance of the 50 mm trace (20 °C) | 97.0 mΩ |
| Voltage drop at external capacity | 85.9 mV |
Assumptions
- IPC-2221 empirical power law I = k·ΔT^0.44·A^0.725 with k = 0.048 (external) and 0.024 (internal).
- Copper thickness 35 µm per oz; resistivity 1.724e-8 Ω·m at 20 °C; no airflow or neighbouring-trace heating modelled.
Limits
- An empirical fit for isolated traces, not a thermal simulation; IPC-2152 is not implemented.
- Temperature rise is above ambient; check your own ambient and fabricator copper tolerance.
Next step
- Find the width for your design current — the capacity above is a maximum for one width, not a target current; enter your own current there.
- Check voltage drop over a long run — heating and voltage drop are separate limits; check both.
Trace Parameters
Current Capacity Results
Quick Reference: Current Capacity (10°C Rise)
| Trace Width | 1oz Ext | 1oz Int | 2oz Ext | 2oz Int |
|---|---|---|---|---|
| 10 mil | 0.88A | 0.44A | 1.46A | 0.73A |
| 20 mil | 1.46A | 0.73A | 2.41A | 1.20A |
| 50 mil | 2.83A | 1.42A | 4.68A | 2.34A |
| 100 mil | 4.68A | 2.34A | 7.74A | 3.87A |
| 200 mil | 7.74A | 3.87A | 12.79A | 6.39A |
*Values are approximate. Use calculator for precise results. (IPC-2221 power-law, 10 C rise, 1 oz = 1.37 mil)
IPC-2221 Current Capacity Formula
Current Capacity Design Tips
Temperature Rise
Lower temperature rise = more conservative design. Use 10°C for general applications, 20°C for space-constrained designs, 5°C for high-reliability applications.
Safety Margin
Always apply a 20-50% safety margin to calculated values. Account for manufacturing variations, ambient temperature, and airflow conditions.
High Current
For currents above 10A, consider using multiple traces in parallel, adding copper planes, or using thicker copper weights (2oz or higher).
Trace width by current and copper weight
Need to Calculate Trace Width?
If you know your required current and want to find the minimum trace width, use our trace width calculator instead.
Current Capacity FAQ
What determines PCB trace current capacity?
Current capacity depends on trace width, copper thickness, layer position (internal vs external), acceptable temperature rise, and ambient conditions. Wider, thicker traces on external layers carry more current.
Why can external layers carry more current?
The IPC-2221 formula uses k=0.048 for external layers and k=0.024 for internal layers, so at the same cross-section an internal trace carries about half the current. External layers can lose heat to air, while internal layers are surrounded by insulating FR-4.
What temperature rise should I use?
Common choices are 10°C (conservative), 20°C (moderate), or 30°C (aggressive). Consider your ambient temperature and reliability requirements when choosing.
How do I handle high current (>10A)?
Options include: wider traces, thicker copper (2oz+), parallel traces, copper planes, thermal vias for heat dissipation, and active cooling in extreme cases.
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