PCB Trace Width Converter
Calculate PCB trace width needed for a given current, or find the current capacity of a trace.
Based on IPC-2221 standards.
Enter current and parameters to calculate required trace width, or enter trace width to find current capacity.
Required Trace Width
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PCB trace width determines how much current a copper trace can safely carry. Too narrow a trace for the current causes overheating and potential board failure.
The IPC-2221 standard formula: The widely used IPC-2221 standard provides this formula for calculating trace width:
- Area (mils^2) = (Current / (k x TempRise^b))^(1/c)
- Width (mils) = Area / (Thickness x 1.378)
Where the constants for external layers are:
- k = 0.048, b = 0.44, c = 0.725
And for internal layers:
- k = 0.024, b = 0.44, c = 0.725
Standard copper thicknesses:
- 1 oz/ft2 = 1.378 mils = 0.035 mm (most common for standard PCBs)
- 2 oz/ft2 = 2.756 mils = 0.070 mm (used for power applications)
- 0.5 oz/ft2 = 0.689 mils = 0.018 mm (thin boards, fine-pitch components)
Quick reference table (external layer, 1 oz copper, 10C temp rise):
| Current (A) | Trace Width (mils) | Trace Width (mm) |
|---|---|---|
| 0.5 | 10 | 0.25 |
| 1.0 | 25 | 0.64 |
| 2.0 | 60 | 1.52 |
| 3.0 | 100 | 2.54 |
| 5.0 | 200 | 5.08 |
| 7.0 | 330 | 8.38 |
| 10.0 | 550 | 13.97 |
Important design considerations:
- The temperature rise value is relative to the ambient temperature. A 10C rise is a conservative, commonly used design target.
- Internal traces have less cooling capacity (surrounded by FR4 insulation instead of air), so they need to be wider for the same current.
- These calculations assume DC or low-frequency current. At high frequencies, skin effect reduces the effective cross-section of the trace.
- For traces carrying high current near other components, consider the overall thermal management of the board.
- Always add a safety margin of at least 20-50% beyond the calculated minimum width.
- Vias used in the current path also have current limitations and may need multiple vias in parallel for high-current connections.
Unit conversions:
- 1 mil = 0.001 inch = 0.0254 mm
- 1 mm = 39.37 mils