Interactive PCB Trace Current Calculator
Estimate how much current a PCB trace can carry, or calculate the trace width required for a target current.
Uses IPC-2221 empirical equations for quick estimation. Final design should be validated with your PCB manufacturer and thermal testing.
What this PCB trace current calculator does
A PCB trace is basically a tiny copper wire printed on your board. If that trace is too narrow for the current it carries, it can overheat, create voltage drop issues, or fail prematurely. This calculator helps you size traces faster by using standard IPC-2221 equations.
You can use this tool in two ways:
- Find maximum current for a known width, copper thickness, and temperature rise.
- Find required width when you already know the current you need to carry.
Formula used (IPC-2221)
The calculator uses the commonly referenced empirical relationship:
- I = k × (ΔT)0.44 × A0.725
- I = current in amps
- ΔT = allowed temperature rise in °C
- A = cross-sectional area in mil²
- k = 0.048 for external layers, 0.024 for internal layers
Trace area is calculated as: A = trace width (mil) × copper thickness (mil). Copper thickness is estimated from copper weight using approximately 1 oz/ft² ≈ 1.378 mil.
Input guide
1) Layer type
External layers dissipate heat to air more effectively, so they can handle more current at the same width. Internal layers are insulated by FR-4 and usually require wider traces for the same current.
2) Copper weight
Heavier copper increases cross-sectional area and reduces resistance. Typical stackups use 1 oz outer layers, while power designs may use 2 oz or more.
3) Temperature rise
A higher allowed temperature rise permits more current in the same trace size, but too much rise can impact reliability and nearby components. Conservative designs often choose 10°C rise for sensitive systems.
4) Trace width or target current
Depending on mode, enter either your existing width or desired current. The tool computes the missing value instantly.
Quick reference suggestions
| Design Situation | Practical Starting Point |
|---|---|
| Low-power logic traces | 6–10 mil, 1 oz copper |
| General power rails | 20–50 mil, verify with current calculator |
| Higher current paths | Use wide pours, thicker copper, and thermal checks |
| Internal high-current routing | Increase width significantly vs. outer layers |
Best practices beyond calculator math
- Check voltage drop, not just temperature rise.
- Use copper pours/planes for power distribution where possible.
- Avoid long narrow bottlenecks near connectors and FETs.
- Pay attention to via current capacity in multi-layer transitions.
- Keep high-current loops short to reduce EMI and losses.
- Validate final design with thermal imaging or prototype measurements.
Important limitation
IPC-2221 is useful for first-pass sizing, but it is still an approximation. Real behavior depends on board thickness, copper balance, airflow, local heat sources, solder mask, and plane coupling. For dense power electronics, consider simulation tools and manufacturer design support before finalizing production.