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A PCB trace carrying too much current for its size heats up, potentially damaging the board or nearby components. This calculator finds the minimum trace width needed to carry a target current without exceeding a safe temperature rise, using the standard IPC-2221 empirical formula. This is a genuinely different design question from trace impedance — this tool is about current-carrying capacity, not signal integrity.
How it works
Enter the target current, the maximum temperature rise you'll allow, whether the trace is on an external (top/bottom) or internal layer, and the copper thickness. The calculator applies I = k × ΔT^0.44 × A^0.725 (solving for area A, then width = A ÷ thickness), using k = 0.048 for external traces or k = 0.024 for internal traces — internal traces need roughly double the width for the same current, since they dissipate heat less effectively buried inside the board.
- Enter current (A).
- Enter allowed temperature rise (°C).
- Enter trace location.
- Enter copper thickness (mils) — e.g. 1.4 for 1oz copper.
- Click Calculate to see your results.
Examples
A moderate-current external trace
Carrying 2A on an external layer with a 20°C allowed temperature rise and standard 1oz (1.37 mil) copper requires a trace about 20.3 mils wide.
Who should use it
- Power electronics and PCB design for current-carrying traces.
- Electronics coursework on PCB design constraints.
Industry applications
- PCB design and electronics manufacturing
- Power electronics and high-current circuit design
Advantages
- Uses the standard, widely-adopted IPC-2221 formula.
- Distinguishes external vs. internal trace requirements, a real and significant difference.
Limitations
- An empirical approximation, not an exact thermal simulation — critical designs should add margin or verify further.
Common mistakes to avoid
- Using the external-trace formula for a buried internal trace, understating the width actually needed.
- Ignoring current-capacity sizing entirely when a trace is also being sized for impedance — both constraints need to be satisfied.
Best practices
- Check both current-carrying capacity AND impedance requirements for any trace carrying meaningful current at a controlled impedance.
- This formula is a widely-used design approximation — verify critical, high-current designs with your PCB fabricator's own tools or additional margin.
Tips
- If a trace carries both meaningful current AND needs controlled impedance, check it against both this calculator and the PCB Trace Impedance Calculator — pick the wider of the two required widths.