What is a PCB trace width calculator?
A PCB trace width calculator helps you estimate the minimum copper trace width required to safely carry a given current on a printed circuit board. With inputs such as current, copper thickness, layer type, temperature rise and trace length, it predicts key parameters like:
- Required trace width for a specified current
- Voltage drop across the trace
- Power loss due to copper resistance
- Total copper area and cross-section
Sizing traces correctly is critical for reliability. Too narrow and traces overheat, drift in resistance, or even delaminate from the board. Too wide and you waste board area that could be used for routing or compact layouts.
Key parameters used by this calculator
Current and copper thickness
The main driver for trace width is how much current the trace needs to carry. Higher current means more I²R losses and heat. Copper thickness (often specified as 1 oz, 2 oz, etc.) defines how much cross-section area you get for a given width:
- 1 oz/ft² ≈ 35 µm thickness
- 2 oz/ft² ≈ 70 µm thickness
For the same current and temperature rise, a thicker copper layer allows a narrower trace.
Temperature rise and ambient conditions
IPC-2221 and similar standards define trace width in terms of a maximum allowed temperature rise (ΔT) above ambient. A typical design target for general electronics is ΔT = 10 °C to 20 °C above a 20–25 °C ambient.
Lower allowed temperature rise (for long-life or tightly packed designs) → wider traces. Higher allowed temperature rise (for short-duty or non-critical circuits) → narrower traces.
Internal vs external layers
External traces on the top or bottom layer dissipate heat more easily thanks to direct contact with air and any copper pour around them. Internal traces are “buried” in the laminate and retain more heat, so for the same current and temperature rise, internal traces generally need to be wider than external traces.
How this calculator works
This calculator uses industry-standard IPC-2221 style equations to estimate the required trace cross-section area and converts that into a minimum width based on your copper thickness. In simplified form, the cross-sectional area A (in mil²) is derived from:
A = ( I / ( k × ΔTb ) )1/c
where:
- I – current (A)
- ΔT – allowed temperature rise (°C)
- k, b, c – empirical constants depending on internal / external layer type
Once A is known, the required trace width is:
Width = A / thickness
with copper thickness expressed in mils (e.g. 1 oz ≈ 1.37 mils).:contentReference[oaicite:0]{index=0}
The results are estimates under standard conditions. Real-world factors like airflow, copper pour, heat-spreading planes and board stackup can allow narrower traces, while potting or poor ventilation may require wider traces.
Quick reference table (1 oz, external layer, ΔT = 10 °C)
The table below shows approximate minimum trace widths for common currents, assuming:
- 1 oz external copper
- 10 °C temperature rise above ambient
- Standard FR-4 in still air
| Current (A) | Approx. width (mils) | Approx. width (mm) | Typical use |
|---|---|---|---|
| 0.5 A | ≈ 5 mils | ≈ 0.12 mm | Low-power logic rails, small loads |
| 1.0 A | ≈ 12 mils | ≈ 0.30 mm | General I/O, small DC motors, LED strings |
| 2.0 A | ≈ 31 mils | ≈ 0.80 mm | DC/DC converter outputs, power rails |
| 3.0 A | ≈ 54 mils | ≈ 1.40 mm | High-current power stages, drivers |
These values are intentionally conservative and should be treated as a starting point. Always check your PCB manufacturer’s minimum trace width capability and add a sensible safety margin (for example +20–50%) for critical power traces.
Design tips for using this calculator
- Separate signal and power routing – Use narrow traces for low-current digital signals, and wider routes or polygons for power paths.
- Use copper pour for high current – For motor drivers or power supplies, consider planes or large pours instead of single traces.
- Think about thermal paths – Place heat-generating components so that heat can escape through copper pours, vias, and airflow.
- Validate critical nets – For high-reliability or safety-critical designs, validate with lab measurements or detailed thermal simulation.
If you are sizing traces for industrial controllers, motor drives, or PLC I/O modules and are not sure which parameters to use, feel free to reach out to our engineering team for application-specific guidance.
