How to use the Track Width and Current Calculator
This calculator helps you determine either the Maximum Current a PCB trace can handle or the Required Width based on an allowable temperature rise. Enter one value, and the calculator determines the other limit based on the allowed temperature rise. The last calculated field will highlight in green for clarity.
Additionally, by entering your specific Application Current (the actual current flowing in your design), you can see the Voltage Drop, Power Loss, and Resistance of that specific track. The calculator accounts for the temperature coefficient of copper at the heated trace temperature.
Use the plots to visualize how your trace behaves near the calculated operating point.
How to Properly Size a PCB Track
Sizing a trace correctly is a critical step in PCB design. It involves checking two main limits: Thermal and Voltage Drop.
- Thermal Limit: The trace must be wide enough to handle the current without overheating and damaging itself or nearby tracks or components. If a track is sufficiently hot, it may act as a fuse and produce a non-controlled open circuit. IPC standards define this width based on an allowable temperature rise (e.g., +10°C).
- Voltage Drop: Even if the trace doesn't burn up, long traces can have enough resistance to drop significant voltage. This can cause the voltage at the load to drop below the required value.
Recommendation: Calculate the width required for both, and use the larger of the two values.
If you need to reduce the trace width due to lack of space, you can put parallel track in another PCB layer so that the current splits among those. In that case, ensure that the vias are properly sized to allow the current to flow through them.
In addition to temperature and voltage drop, track inductance is also critical for high-frequency signals such as those present in switching power supplies, digital signals or RF signals. Inductance is minimized by widening the trace and making it as short as possible (also ensure that there is a path for the current to return just beneath the trace without any obstacles).
In general, make traces as short as possible and as wide as possible.
IPC-2221 Thermal model
IPC-2221 is the generic standard on printed board design. Its thermal model is essentially a curve-fitting match to a set of charts from the 1950s (originally for MIL-STD-275), making it a conservative standard. The formula is:
$$ I = k \cdot (\Delta T)^{0.44} \cdot A^{0.725} $$
Where:
- I = Maximum Current [Amps]
- ΔT = Temperature Rise [°C]
- A = Cross-sectional Area [mils²]
- k = Derating constant (0.048 for external, 0.024 for internal layers)
This method is very conservative. It assumes a single track in air and ignores the heat-sinking capabilities of modern board materials and copper planes. The data for the newer IPC-2152 standard is based on more accurate and representative for real circuits test setups, but it does not provide a single algebraic formula for calculation. Thus, IPC-2221 provides a safe, easy-to-calculate baseline. If you have enough space on the PCB, go with it. If you are in a situation with high currents and temperatures, consider making a detailed analysis with finite elements analysis (FEA) and Always verify critical designs with thermal testing.
Frequently Asked Questions
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Should I make the trace exactly as wide as the calculator says?
You can, but it is always better to go as wide as reasonable to reduce trace resistance and inductance, which cause voltage drop and signal integrity issues. -
Should I use IPC-2221 for high-current designs?
For high-current or critical power designs, IPC-2221 can be overly conservative, leading to traces wider than necessary. IPC-2152 allows for more optimization but is harder to calculate manually. For most standard signals and moderate power, IPC-2221 is a safe starting point. -
How does trace length affect max current?
According to IPC-2221, trace length does not significantly affect thermal current capacity, which depends on cross-sectional area and heat dissipation. However, longer traces increase resistance and voltage drop linearly. In real circuits, the dynamics are more complex and the geometry of the trace can affect the maximum current. -
What is "1 oz" copper?
It is a weight-based measurement: 1 ounce of copper rolled out to cover 1 square foot. This results in a thickness of approximately 1.37 mils or 35 µm. -
Do vias handle the same current as traces?
No. A via acts like a small internal cylinder. To match the current capacity of a wide trace, you often need multiple vias stitched together (a "via fence" or array) to lower the effective resistance and Inductance.