PCB Trace Width Calculator
Minimum trace width for a current and temperature rise, with resistance and voltage drop.
What it does
Finds the minimum copper trace width that carries a current without heating more than you allow, using the IPC-2221 relationship. It also reports the trace’s resistance, voltage drop and power loss.
Where it's used
Power traces, motor and LED driver outputs, and any trace carrying more than a few hundred milliamps.
How to use it
- Enter the current and the temperature rise you accept (10 °C is conservative).
- Choose the copper weight from your PCB stack-up.
- Choose whether the trace is on an outer or an inner layer.
- Enter the length to see resistance and voltage drop.
The formula explained
- I
- current in the trace
- ΔT
- allowed temperature rise above ambient
- A
- copper cross-section, in mil²
- k
- 0.048 for outer layers, 0.024 for inner layers
- t
- copper thickness: 1 oz ≈ 35 µm
Worked example
5 A on an inner layer of 2 oz copper, allowing a 20 °C rise.
Inputs:
- Current: 5 A
- Allowed temperature rise: 20 °C
- Copper weight: 2 oz (70 µm)
- Layer used for drop calculation: Internal (inner)
- Ambient temperature: 40 °C
- Trace length: 80 mm
The calculator gives:
- External layer width: 0.913 mm
- Internal layer width: 2.376 mm
- Cross-section (ext.): 98.5 mil²
Tips and common mistakes
- Inner layers cool poorly and need much wider traces than outer layers.
- Long traces may be limited by voltage drop rather than heating.
- Copper pours and heavier copper help when width is limited.
Questions people ask
What formula does the calculator use?
IPC-2221: I = k × ΔT^0.44 × A^0.725, with A in square mils and k = 0.048 for outer layers or 0.024 for inner layers. The calculator solves it for the cross-section and turns that into a width for your copper thickness.
What does 1 oz copper mean?
One ounce of copper spread over one square foot, which is about 35 µm (1.4 mil) thick. 2 oz copper is about 70 µm and carries roughly twice the current at the same width.
Is IPC-2221 still the right standard?
It is the classic one and errs on the safe side. The newer IPC-2152 is based on fresh measurements and often allows narrower inner-layer traces, so widths from this calculator are conservative.
Reference: IPC-2221 / 2152
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