PCB Trace Width Calculator
Estimate the minimum copper trace width needed to safely carry current using the IPC-2221 method.
What this PCB current trace calculator does
This tool estimates the minimum trace width required on a printed circuit board so a copper trace can carry your target current without exceeding a chosen temperature rise. It also provides a recommended width with design margin and, when trace length is entered, a rough estimate of resistance, voltage drop, and power loss.
How the calculation works
The calculator uses the classic IPC-2221 empirical relationship:
I = k × (ΔT)0.44 × (A)0.725
Where:
- I = current in amperes
- ΔT = allowable temperature rise in °C
- A = copper cross-sectional area in mil²
- k = 0.048 for external layers, 0.024 for internal layers
Once area is found, trace width is derived from: Width = Area ÷ Copper Thickness. Copper thickness is based on oz/ft² input.
Input guide
1) Current
Use worst-case continuous current, not average only. If surge or startup current matters, design for that stress too.
2) Temperature rise
Lower allowed rise means wider traces. If reliability is important, staying conservative (for example 10°C rise) is usually smart.
3) Copper weight
Thicker copper allows narrower traces for the same current. Typical values are 1 oz, 2 oz, and 3 oz.
4) Layer type
Internal traces cool less effectively than external traces, so they generally need to be wider for the same current.
Practical PCB design tips for current-carrying traces
- Use wider traces than the absolute minimum whenever space allows.
- Prefer short, direct current paths to reduce voltage drop and heating.
- Add copper pours or polygons for power rails.
- Use multiple vias in parallel when transitioning high current between layers.
- Check connector, fuse, and terminal ratings; trace width is only one part of the current path.
- Verify manufacturer minimum trace/space rules and copper tolerances.
Example
Suppose you need 3 A on an external layer, 1 oz copper, with 10°C allowable rise. The calculator returns a minimum width in mil and mm, then adds your chosen margin (for example +25%) to provide a practical target width.
You can then compare that width with available routing space. If routing is tight, options include increasing copper weight, moving to external routing, reducing path length, or splitting current across multiple traces.
Bottom line
A PCB trace width calculator helps you quickly size traces for current carrying capacity, estimate thermal rise impact, and catch voltage-drop problems early. Use this as your first pass, then confirm with board-level thermal checks and real measurement in prototype testing.