PCB Trace Width Calculator
Estimate the minimum copper trace width needed to carry current, based on the IPC-2221 empirical model.
Note: This tool provides a practical estimate. For high-reliability, high-frequency, or thermally constrained designs, validate with IPC-2152 data, simulation, and your board manufacturer.
Why trace width matters in PCB design
Copper traces are the “wires” on your PCB. If a trace is too narrow for the current it carries, it heats up, increases resistance, and can fail over time. If it is too wide, you may waste board space and make routing harder than necessary.
A good trace width is a balance between thermal performance, electrical loss, manufacturability, and layout density. This calculator helps you quickly estimate a safe starting width.
What this PCB width calculator uses
The calculator uses the IPC-2221 current-carrying trace formula:
where:
I = current (A), ΔT = temperature rise (°C), A = trace cross-sectional area (mil²)
k = 0.048 for external layers, 0.024 for internal layers
We solve this equation for area, then divide by copper thickness to get minimum width. The calculator displays the result in both mil and mm, and also estimates resistance and voltage drop when trace length is provided.
How to use it
1) Enter current
Use the expected steady-state current in amps for the trace. If your load is pulsed, design for RMS or worst-case continuous equivalent unless you have thermal characterization.
2) Choose temperature rise
Lower temperature rise means a wider trace. Common design choices are 10°C to 20°C depending on environment and reliability goals.
3) Set copper thickness
1 oz copper is common in many standard PCBs. Heavier copper allows narrower traces for the same current, but can affect cost and minimum manufacturable features.
4) Select internal vs external layer
External layers cool better due to airflow and radiation, so they can carry more current at the same width versus inner layers.
5) Add length for voltage-drop estimate
Longer traces have higher resistance and bigger voltage drop. This is especially important for low-voltage power rails (e.g., 1.2V, 3.3V, 5V).
Practical design tips
- Add margin: After calculating, round up your width to a practical DRC-friendly value.
- Check bottlenecks: Neck-downs near pads can dominate heating and voltage drop.
- Use pours/planes: For power rails, copper pours often outperform narrow traces.
- Mind vias: High current paths may need multiple vias in parallel between layers.
- Verify with fabrication limits: Confirm minimum/typical trace and spacing rules with your board house.
Example scenario
Suppose your trace carries 2 A on an external layer, with 1 oz copper and a 10°C allowed rise. The calculator will return a width in the tens of mil range. If that is too wide for your layout, you can:
- Increase copper thickness (e.g., from 1 oz to 2 oz)
- Use an external layer instead of internal routing
- Route with parallel traces or copper pours
- Lower resistive losses by shortening path length
Limitations and engineering judgment
This is a strong first-pass tool, but not the final word. Real-world thermal behavior depends on board stack-up, nearby copper, airflow, substrate properties, and duty cycle. For mission-critical or high-power designs, use lab measurements or thermal simulation and compare against IPC-2152 guidance.
Quick FAQ
Is IPC-2221 still useful?
Yes, for quick estimates and early design decisions. IPC-2152 provides more modern, detailed guidance for many cases.
Should I always choose the calculated minimum width?
No. Treat it as a minimum baseline. In many designs, adding width improves reliability and reduces voltage drop at low cost.
What about AC or high-frequency signals?
This calculator targets DC/low-frequency current capacity. Controlled impedance and skin effect require different calculations.