This calculator uses the industry-standard IPC-2221 generic formula to determine the minimum track width required to carry a specific current without exceeding the temperature rise limit.
Note: IPC-2221 is a conservative standard. For more complex stack-ups or high-density designs, the newer IPC-2152 standard is recommended.
First, calculate the required Cross-Sectional Area (A):
Area [mils²] = (Current [Amps] / (k × TempRise^0.44)) ^ (1/0.725)
Then, calculate the Width (W):
Width [mils] = Area / (Thickness [oz] × 1.378)
Constants (k):
- External Layers: k = 0.048
- Internal Layers: k = 0.024 (Requires wider traces due to heat trapping)
What is "Temperature Rise"?
It is how much hotter the trace is allowed to get compared to the ambient air. A standard safe value is 10°C. If you allow 20°C rise, you can use a thinner trace, but it will get hotter.
External vs. Internal Layers?
External traces (Top/Bottom) are exposed to air, so they cool down better. Internal traces are sandwiched inside the board (FR4), so they retain heat and must be roughly 2x wider for the same current.
What is "1 oz" copper?
It refers to the thickness of the copper foil. 1 oz/ft² ≈ 1.37 mils ≈ 35 micrometers (µm). This is the most common standard thickness.
Why is the required width so large?
High current requires wide traces to prevent overheating. To reduce width, try increasing copper thickness (e.g., 2oz), using a Polygon Pour (copper plane), or routing on external layers.
Should I worry about voltage drop?
Yes, for long traces or low-voltage sensitive power rails (e.g., 3.3V or 1.2V). Input the trace length above to check if the drop is acceptable (usually < 3%).