PCB Trace Width Calculator

IPC-2221 trace width for a target current and temperature rise, for internal and external copper layers.

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width (mils)

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width (mm)

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area (mils²)

How PCB trace width is calculated

This calculator uses the IPC-2221 standard to estimate the minimum copper trace width needed to carry a given current without exceeding a chosen temperature rise above ambient. External (outer) layers dissipate heat more easily than internal (inner) layers, so they can run narrower for the same current.

Formula (IPC-2221)

area = ( I / (k · ΔT^0.44) )^(1 / 0.725)
width = area / (thickness_oz · 1.378)

k = 0.048  (external / outer layers)
k = 0.024  (internal / inner layers)

I is current in amps, ΔT is the allowed temperature rise in °C, area is in mils², and 1 oz/ft² of copper is about 1.378 mils thick.

Notes & limits

IPC-2221 is conservative and intended for currents up to ~35 A and traces up to ~400 mils wide.
It ignores nearby copper pours, vias, and airflow — treat the result as a floor, then add margin.
For high-current or safety-critical designs, follow IPC-2152 and your fab's guidance.

FAQ

What temperature rise should I use?

10 °C is a common conservative default; 20–30 °C is used when board temperature headroom allows.

Internal vs external — which is wider?

Internal layers need a wider trace for the same current because they trap more heat.