PCB Trace Width Calculator
Estimate minimum copper trace width from current, allowable temperature rise, copper weight, and layer type using the IPC-2221 approximation.
where k = 0.048 (external) or 0.024 (internal), b = 0.44, c = 0.725.
Why PCB trace sizing matters
A printed circuit board trace is a conductor, and every conductor has resistance. If the trace is too narrow for the current you run through it, it heats up more than expected. That can cause voltage drop, reliability issues, and in extreme cases board damage. A good PCB trace width calculator gives you a fast starting point so your copper geometry matches your electrical and thermal requirements.
This is especially important in power electronics, motor drivers, battery-powered devices, LED lighting, and any design with sustained current.
How this calculator works
This tool uses the widely known IPC-2221 empirical model to estimate required cross-sectional area, then converts that area into minimum trace width based on copper thickness.
Inputs
- Current (A): Expected continuous current through the trace.
- Temperature rise (°C): Maximum copper temperature rise above ambient you allow.
- Copper weight (oz/ft²): Determines copper thickness.
- Layer type: Internal traces cool less effectively than external traces, so they require more area.
- Length (mm): Used to estimate resistance, voltage drop, and power dissipation.
Outputs
- Required minimum trace width in mil and mm
- Rounded-up practical width value
- Cross-sectional area and current density
- Optional electrical effects: resistance, voltage drop, and I²R loss
Practical design guidance beyond the math
A calculator result is your baseline, not always your final number. In real boards, thermal behavior depends on copper pours, airflow, neighboring hot parts, solder mask, and via stitching. For robust designs, consider using a wider trace than the minimum.
- Add margin: 20–100% extra width is common in production designs.
- Check fabrication limits: Your board house may specify minimum trace/space (for example 4/4 mil or 6/6 mil).
- Use planes when possible: For high current, copper pours or planes are usually better than narrow traces.
- Parallel paths: Multiple traces or polygon routing can reduce resistance and heating.
- Via current capacity: If current switches layers, make sure vias are sized and multiplied appropriately.
Internal vs external trace width
External layers shed heat more efficiently to air, so they can carry more current at the same width and temperature rise. Internal layers are thermally insulated by surrounding dielectric and need larger cross-sectional area for equal performance. If your path includes both internal and external sections, size to the worst-case segment.
Example use case
Suppose you need to route 2 A on 1 oz copper with a 10°C rise. Select external and calculate. You will get a recommended width and can then compare that to your layout constraints. If space permits, go wider to reduce drop and improve thermal margin.
Important note on standards
IPC-2221 is popular for quick calculations, but modern thermal behavior can differ depending on stackup and environment. For critical designs, validate with your PCB manufacturer data, IPC-2152 guidance, simulation, and prototype testing.
Quick PCB trace checklist
- Define worst-case continuous current, not average only.
- Set realistic ambient and allowable rise.
- Choose copper weight early in stackup planning.
- Size traces, vias, connectors, and terminals as one current path.
- Review voltage drop budget for low-voltage rails.
- Run thermal verification on dense/high-power areas.