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PCB Trace Width Calculator (IPC-2221)

Enter values with SI prefixes, e.g. 4k7 · 4.7u · 1.2M · 10K

Required PCB trace width for a given current and allowed temperature rise, using the IPC-2221 formula.

Design conditions

Results

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How it works

IPC-2221 is an empirical formula that gives the conductor cross-section needed for a given current and temperature rise. Outer layers can radiate heat to air and have a k value twice as large, so inner layers need a wider trace for the same current.

A (mil²) = (I / (k × ΔT0.44))1/0.725
Thickness (mil) = oz × 1.378
Width (mil) = A / thickness
Width (mm) = Width (mil) × 0.0254
k: 0.048 outer layer, 0.024 inner layer

Worked example

With 1 A, a 10 °C rise and 1 oz copper on an outer layer, the required cross-section is about 16.3 mil². The width is about 11.8 mil, or about 0.30 mm. On an inner layer under the same conditions, the required cross-section is about 2.6 times larger.

Design tips

  • Size the trace for the larger of the continuous and peak currents, and keep at least a 30 % margin.
  • For high-current paths use 2 oz copper or a copper pour, and connect layers with several vias.
  • Inner-layer traces have fewer ways to shed heat, so design them wider than outer-layer traces for the same current.
  • A narrow trace has higher resistance and an IR voltage drop. For long power lines, also calculate the voltage drop.

Limitations

  • IPC-2221 is an older, conservative model and can call for a wider trace than the real current capacity needs. The newer IPC-2152 standard reflects board thickness and nearby copper area more accurately.
  • The formula assumes natural convection in air. Forced airflow or nearby heat sources change the temperature rise.
  • Impedance control for high-frequency signal lines is outside this calculation and needs a separate analysis.

Frequently asked questions

Should I use IPC-2221 or IPC-2152?

IPC-2221 is an older empirical formula and usually gives a conservative, wide trace. IPC-2152 accounts for board thickness and nearby copper, so it is more precise but more complex. Use the IPC-2221 result for conservative design, and IPC-2152 when you need to reduce copper area.

What temperature rise should I allow?

A rise of 10 to 20 °C is commonly allowed. Set the final value by considering the ambient temperature, the maximum operating temperature and nearby heat sources.

Do I also need to check the voltage drop?

Yes. Even with an adequate width, a long supply line has an IR drop from its resistance. Calculate the trace resistance from its length and compare the drop with the allowed voltage drop.