Electronics / PCB
PCB Trace Width Calculator (IPC-2221)
Find the minimum width of a printed circuit board trace for a given current, allowed temperature rise, copper weight, and layer, using the IPC-2221 formula, with the trace's resistance and voltage drop.
PCB Trace Width Calculator (IPC-2221): IPC-2221 relates current to the trace's cross-section: I = k × ΔT^0.44 × A^0.725, with A in square mils, k = 0.048 on outer layers and 0.024 on inner layers. The area is divided by the copper thickness (1.378 mil, or 35 µm, per ounce) to get the width. For 1 A, a 10 °C rise, and 1 oz copper on an outer layer, that is about 11.8 mil, or 0.30 mm. Runs 100% locally in your browser with zero server file uploads.
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The IPC-2221 formula: current = k × ΔT^0.44 × area^0.725, with the area in square mils and k = 0.048 for outer layers, 0.024 for inner layers, which shed heat less well. It is a conservative starting point; the newer IPC-2152 charts often allow narrower traces. Leave a margin, and widen power traces wherever there is room.
Worked examples
At 1 oz copper on an outer layer with a 10 °C rise: 0.5 A needs about 4.5 mil, 1 A about 11.8 mil, 2 A about 30.8 mil, and 3 A about 54 mil. With 2 oz copper each width halves.
For wires leaving the board, the wire gauge converter gives cable sizes and resistance.
Practical tips
Fabricators set a minimum width and gap, often 5 or 6 mil for standard boards; the current-based width is a minimum on top of that. Use copper pours or several vias for high currents and wide traces to connectors.
Short traces to power pins benefit from extra width even at low current, because it lowers their resistance and inductance.
How to use it
- Enter the current the trace carries and how much it may warm up.
- Enter the copper weight, usually 1 oz/ft², and choose an outer or inner layer.
- Read the minimum width in mils and millimetres; add the length for its resistance.
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Frequently asked questions
What temperature rise should I allow?
10 °C is a common conservative choice; 20 °C is often acceptable. Hotter traces raise the board's temperature and the resistance of the copper.
Why are inner layers wider?
Inner traces are surrounded by board material and lose heat more slowly, so the formula halves k, which needs about 2.6 times the width.
Is IPC-2221 the latest standard?
IPC-2152 replaced it with more detailed charts that often allow narrower traces; IPC-2221 remains a widely used, conservative starting point.
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