Free PCB Trace Current Calculator
External traces dissipate heat better and can carry more current
Standard PCB trace widths range from 6 mil to 500 mil
Standard copper weight: 1 oz/ft² ≈ 1.37 mil (35 µm)
Typical allowable rise: 10°C to 20°C for most designs
Operating environment temperature around the PCB
Optional - enables resistance, voltage drop, and power dissipation results
Enter trace width, thickness, and temperature rise to calculate current capacity
Designing a printed circuit board involves many trade‑offs, and one of the most critical is ensuring that each conductor can safely carry the intended current without overheating. The PCB trace current calculator (often called a PCB ampacity calculator or trace width calculator) is a free online tool that helps you determine the maximum current a given trace can handle. By accounting for trace geometry, layer placement, and temperature limits, this calculator supports both internal and external routing configurations.
Why Trace Ampacity Matters
A trace’s current capacity is fundamentally determined by its cross‑sectional area (width × thickness) and the allowable temperature rise above ambient. Exceeding this limit can cause delamination, solder joint failures, or even fire. Using this tool early in the design process lets you verify that your trace dimensions meet the required circuit board trace current without resorting to over‑engineering or costly board revisions.
Input Parameters
To obtain a current rating, you provide the following primary inputs:
- Trace location – whether the trace lies on an outer layer (external) or an inner layer (internal). Internal traces dissipate heat less effectively, so they carry less current for the same geometry.
- Trace width – the lateral dimension perpendicular to current flow.
- Trace thickness – the copper foil height (e.g., 1 oz/ft² copper roughly equals 35 µm).
- Maximum desired temperature rise – the difference between the trace’s operating temperature and the ambient temperature, typically ranging from 10 °C to 100 °C.
Optionally, you can enter the ambient temperature and the trace length. Once these values are supplied, the calculator delivers:
- Max current (the ampacity)
- Cross‑sectional area (width × thickness)
- Operating temperature (ambient + rise)
- Resistance of the trace
- Voltage drop (computed via Ohm’s law)
- Power dissipation
More Than a Current Capacity Tool
Beyond simply answering “how much current can a PCB trace carry,” this calculator simultaneously computes the trace’s electrical resistance, voltage drop at the maximum current, and the power dissipated as heat. This gives you a complete electrical profile of the trace, enabling you to check whether voltage drop and thermal output stay within acceptable limits for your application.
Flexible and Instant Results
The PCB trace current calculator accepts any combination of inputs you choose to fill in. As soon as sufficient data is entered, it automatically populates the remaining fields, saving you from manual recalculations. There is no fixed order, so you can start from either the geometry details or a desired current target.
FAQ
1. What primary inputs are required for the PCB trace current calculator?
You must specify the trace location (internal or external), trace width, trace thickness, and the maximum allowed temperature rise above ambient. Optionally, you can also enter the ambient temperature and trace length.
2. What additional outputs does the calculator provide besides maximum current?
Along with the maximum current, the tool returns the trace’s cross-sectional area, operating temperature, resistance, voltage drop, and power dissipation at that current level.
3. Why do internal traces have a lower current capacity than external traces?
Internal traces are embedded within the board and have poorer heat dissipation compared to external traces. For the same width, thickness, and temperature rise, an internal trace can typically carry only about half the current that an external trace can handle.
4. Can I use the calculator in any order of inputs?
Yes. The tool accepts any sequence of inputs; once enough data is provided, it automatically computes and fills the remaining fields. No strict input order is required.
How to Use
- Enter the trace parameters: width, thickness, temperature rise, and ambient temperature.
- Optionally, enter the trace length to enable resistance, voltage drop, and power dissipation calculations.
- View the calculated maximum current and detailed breakdown of electrical characteristics.