PCB design glossary
Trace
AKA: traces
A copper line on a PCB that carries a signal between two or more pads.
A trace is the physical copper line that implements a net on a PCB layer. Its width determines how much current it can safely carry; its geometry determines how it behaves at high speed.
Confusingly, "trace" and "net" are sometimes used interchangeably even though they're not the same: a single net is usually made up of several physical traces (and sometimes vias) connecting all the pins on that net.
How wide should a trace be?
Width sets how much current a trace can carry before it heats up. IPC-2221 gives the classic formula: on an outer layer with 1 oz copper, about 0.3 mm (12 mil) carries 1 A for a 10 °C temperature rise. Inner layers cool worse and need roughly two and a half times the width for the same current. Thicker copper (2 oz) carries more in the same width.
For signals that carry almost no current, width is set by what the fab can make and by impedance. Many low-cost fabs build 0.127 mm (5 mil) trace and space on standard boards; 0.15 to 0.25 mm is a comfortable default for signals.
Trace layout habits that matter
- Keep power and ground traces short and wide, or use planes instead.
- Route high-speed traces over a solid ground plane, never across a split in it.
- Match impedance where the interface requires it (USB, Ethernet, RF): width and stack-up set it.
- Use 45-degree bends. Right angles are rarely an electrical problem at hobby speeds, but they are harder to etch cleanly and look careless.
- Leave clearance to other copper that your fab's rules allow, and more near high voltage.
Work it out with a free tool
How wide does this trace need to be?
It depends on the current, the copper weight and how much heating you accept. The trace width calculator works it out with IPC-2221 for outer and inner layers.
Calculate trace width