How to Choose Trace Width and Spacing
Estimated reading time: 7 minutes
Two questions trip up almost every beginner: how wide should my traces be? and how much gap do I leave between them? Get them roughly right and your board is reliable and easy to manufacture. This guide gives you safe defaults, a quick current table, and explains how Protoboard Designer's Design Rule Check (DRC) backs you up.
For a typical hobby signal, 0.25 mm (10 mil) traces with 0.2 mm (8 mil) gaps are a safe, fab-friendly default. Make power and ground traces wider. When in doubt, go a little wider.
Why trace width matters
A copper trace has resistance. Push current through it and it warms up and drops a little voltage. Wider (and thicker) copper = lower resistance = more current with less heating. So:
- Signals (buttons, data, sensor lines) carry tiny currents — thin traces are fine.
- Power and ground carry the real current — make these wider.
Most hobby boards use 1 oz copper (about 35 µm thick), which is the standard default at every fab.
A practical width-for-current table
These are conservative rules of thumb for external copper traces on 1 oz copper, allowing a modest ~10 °C temperature rise. They're based on the IPC-2221 guidelines.
| Current | Minimum width | Comfortable width |
|---|---|---|
| Up to 0.5 A | 0.25 mm (10 mil) | 0.3 mm (12 mil) |
| 1 A | 0.5 mm (20 mil) | 0.8 mm (32 mil) |
| 2 A | 1.0 mm (40 mil) | 1.5 mm (60 mil) |
| 3 A | 1.5 mm (60 mil) | 2.0 mm (80 mil) |
Real capacity depends on copper weight, whether the trace is internal or external, how long it is, and how much heat you'll tolerate. For anything carrying serious current, plug your numbers into a free trace width calculator (search "IPC-2221 trace width calculator"). When unsure, wider is safer.
Spacing and clearance
Clearance is the gap between two separate pieces of copper (two traces, or a trace and a pad). Two reasons it matters:
- Manufacturing — the factory can only etch gaps so small. Most hobby fabs reliably do 0.15 mm (6 mil); 0.2 mm (8 mil) is a comfortable, cheap default.
- Voltage — higher voltages can arc across small gaps. For low-voltage projects (3.3 V / 5 V) the manufacturing limit dominates. For mains or high voltage, you need much larger, regulated clearances — research those separately.
Every manufacturer publishes a capabilities page listing its minimum trace width and spacing. If you've picked a fab, set your defaults to match (or stay just above) its limits.
Let DRC catch mistakes
Protoboard Designer includes a Design Rule Check that flags exactly these problems before you order. Its rules include:
- Minimum trace width — traces thinner than allowed
- Minimum trace spacing and copper clearance — copper placed too close together
- Minimum drill size and drill spacing — holes too small or too close
- Minimum annular ring — too little copper around a drilled hole
- Minimum pad size — pads smaller than reliable
Open the Net Probe tool (left toolbar) and choose Run DRC check before exporting, then clear the warnings. It turns "I hope this manufactures" into "I checked."
The annular ring is the copper collar around a drilled hole (pad diameter minus drill, divided by two). Too thin and the drill can break out of the pad. If DRC flags it, make the pad bigger or the drill smaller.
Quick checklist
- Signals: 0.25 mm (10 mil) is plenty.
- Power/ground: size from the current table above, then add margin.
- Gaps: 0.2 mm (8 mil) default; never below your fab's minimum.
- Run DRC and fix every warning before export.