PCB Trace Width
IPC-2221 trace width for a current and temperature rise.
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The engineering
The venerable IPC-2221 curves: empirical, conservative, and still the default answer. Internal layers get half the k because they can't convect — roughly twice the width for the same rise.
For high current or dense boards, IPC-2152 (2009) supersedes this with real measured data including board material and nearby copper; treat this card as the safe first pass.
Where this math comes from
Paul Eisler etched the printed circuit in wartime London (1936–43), and by the 1950s the US military needed rules for how much copper carries how much current — the charts landed in MIL-STD-275 (1950s), migrated to IPC-D-275, and became IPC-2221 (1998). The k·ΔT^0.44·A^0.725 fit on this card is a curve-fit of those 1950s NBS measurements.
IPC-2152 re-measured everything in 2009 with modern boards — the old curves turned out conservative, which for a default is the right direction to be wrong.
- 1943Paul EislerThe etched printed circuit board.
- 1954NBS / military standardsOriginal current-capacity charts (later MIL-STD-275).
- 1998IPCIPC-2221 generic design standard carries the classic curves.
- 2009IPCIPC-2152 replaces them with measured modern data.
See the full timeline of the math behind every calculator →
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