PCB Trace Width Calculator
IPC-2221 compliant trace width for a given current, temperature rise, copper weight, and layer position. Returns width in millimetres and mils plus cross-sectional area.
Size a PCB trace for the current it has to carry without overheating. Enter the current, the temperature rise you'll allow, the copper weight and whether the trace is on an outer or inner layer, and the calculator returns the minimum trace width in millimetres and mils plus the copper cross-section — following the IPC-2221 current-capacity charts.
curl -X POST https://toolsamurai.com/api/v1/pcb-design/pcb-trace-width \ -H "Authorization: Bearer sk_live_•••••••••••••••" \ -H "Content-Type: application/json" \ -d '{ "current_a": 3.5, "temp_rise_c": 10, "copper_weight_oz": 1, "layer": "outer" }'
The method behind the numbers
IPC-2221 relates allowable current to copper cross-sectional area and temperature rise with the empirical curve I = k × ΔT^0.44 × A^0.725, where A is the cross-section in square mils and k is a constant that differs by layer: about 0.048 for external traces (which shed heat to air) and 0.024 for internal traces (which can't). Solving for area and dividing by the copper thickness gives the required width.
Copper weight sets the thickness — 1 oz/ft² is roughly 1.37 mils (34.8 µm), and the tool scales linearly from there. Because inner layers use half the constant, they need noticeably wider traces for the same current. IPC-2221 is the classic, conservative standard; the newer IPC-2152 accounts for board thermal conductivity and plane proximity and often gives different (sometimes narrower) results for modern stackups.
See it in practice
A typical power trace on a standard two-layer board.
- current_a
- 3.5
- temp_rise_c
- 10
- copper_weight_oz
- 1
- layer
- outer
Shows how much wider a buried trace must be for identical current.
- current_a
- 3.5
- temp_rise_c
- 10
- copper_weight_oz
- 1
- layer
- inner
Frequently asked questions
What temperature rise should I allow?
10 °C is a common, conservative default. 20 °C is acceptable when the board has thermal headroom. The rise is above ambient, so factor in how hot the enclosure already runs.
Why do inner-layer traces need to be wider?
An inner trace is buried in FR-4, which is a poor conductor of heat, so it can't shed warmth to air like an outer trace. IPC-2221 captures this by halving the constant, which roughly doubles the area — and therefore width — needed for the same current.
Is IPC-2221 or IPC-2152 better?
IPC-2221 (used here) is the long-standing, conservative reference and is fine for most hobby and general designs. IPC-2152 is more accurate for modern boards because it models dielectric thermal conductivity and nearby copper planes — worth using for dense, high-current, or thermally critical layouts.
Does this account for vias or connectors?
No — it sizes the trace itself. Vias carrying significant current need their own sizing (number and barrel area), and connector/pad heating is separate. Treat this as the trace minimum, then check the rest of the path.
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