// pcb_trace.md

PCB trace width.

Minimum trace width for a given current — IPC-2221 standard. External vs internal layer. Copper weight + max temp rise.

// input.md
// result.md
min trace width — —
cross-section area —
trace resistance —
voltage drop —
power dissipated —
recommendation

// how_it_works.md

IPC-2221 formula

The industry standard for PCB trace current capacity:

A = (I / (k × ΔT^0.44))^(1/0.725)

where:
  A  = cross-section area (mil²)
  I  = current (A)
  ΔT = temp rise (°C)
  k  = 0.048 for external, 0.024 for internal

width (mil) = A / (copper_weight_oz × 1.378)

Then convert mil → mm: width_mm = width_mil × 0.0254

Quick reference (1 oz copper, external, 10°C rise)

  • 0.5 A — 0.25 mm (10 mil) — signal lines
  • 1 A — 0.5 mm (20 mil) — typical 5V rail
  • 2 A — 1.0 mm (40 mil) — small motor / LED strip
  • 5 A — 2.5 mm (98 mil) — big LED array, dev board power
  • 10 A — 5.5 mm (215 mil) — battery feed, switching reg

Gotchas

  • Pour copper for power — for big currents, use a copper pour or plane instead of trying to make a wide trace.
  • Via current limits — vias don't carry as much current as traces. Use multiple parallel vias for power transfer between layers.
  • Connector + pad bottlenecks — your trace is sized for X amps but the pad/connector is rated for Y. Whichever is lower wins.
  • Air vs board temp — IPC-2221 assumes still air. Enclosed PCBs run hotter — go up a copper weight or add airflow.