How wide a PCB trace needs to be is set by the current it carries and how warm you will let it run. Using the IPC-2221 curve, a 2 A trace at a 10 °C rise on 1 oz outer-layer copper wants about 31 mil, roughly 0.78 mm. Set your own below.
Inputs
Result
30.8
mil minimum width
≈ 0.78 mm. This is the IPC-2221 minimum; go wider for margin.
In millimetres
0.78 mm
The formula
IPC-2221 fits a curve to measured data: I = k · ΔT0.44· A0.725, where A is the trace cross-section (width × copper thickness) in square mils, ΔT is the temperature rise you allow, and k captures cooling (Association Connecting Electronics Industries, IPC-2221). Solving for the width: pick a current and a rise, get the cross-section, then divide by the copper thickness. Outer copper is usually about 1.4 mil per ounce.
External vs internal
An outer-layer trace sits in air and sheds heat, so it can be narrower; an inner-layer trace is buried in laminate with nowhere for the heat to go, so it needs more copper for the same current. The constant k carries this: 0.048 external, 0.024 internal. The toggle switches between them. Letting the trace run warmer also lets it be narrower, since the formula trades width against temperature rise.
From a real board
On the OTD L1.03 WS2812 board the strip’s 5 V power comes in on a dedicated injection terminal and runs across the board to the output. The screw terminals handle far more current than the copper does, so the board trace is the real limit and it is sized for the strip’s worst-case current with exactly this calculation (One Thousand Drones, L1.03 design 2026). A strip that draws amps needs real copper, not a signal trace. See the WS2812 driver course.
Treat it as a floor, not a target
IPC-2221 gives a conservative minimum from old, broad data. It does not know about a nearby hot regulator, a via that pinches the current, or a plane that helps spread the heat. Use it to find the floor, then widen for margin where you have the room, and use a poured copper area rather than a skinny trace for a high-current rail.
References
- IPC. IPC-2221, Generic Standard on Printed Board Design (the current-capacity curves this calculator fits).
- DigiKey. PCB trace width conversion calculator (the same IPC-2221 formula and constants).
- One Thousand Drones. WS2812 driver (L1.03), 5 V injection traces. Build the board.