PCB trace width and current: how wide must a trace be?
A practical table based on IPC-2221, the effect of copper weight and layer, and the manufacturing limits to respect.
The question behind the table
A trace heats up when current flows through it. The real question is not when it burns but how much temperature rise is acceptable. IPC-2221 provides the formula; designers usually aim for a rise of about 10 °C above the ambient temperature.
Guide values for a 10 °C temperature rise
| Trace width | 35 µm, outer layer | 35 µm, inner layer | 70 µm, outer layer |
|---|---|---|---|
| 0.15 mm | 0.6 A | 0.3 A | 1.0 A |
| 0.25 mm | 0.9 A | 0.4 A | 1.5 A |
| 0.5 mm | 1.5 A | 0.7 A | 2.4 A |
| 1 mm | 2.4 A | 1.2 A | 4.0 A |
| 2 mm | 4.0 A | 2.0 A | 6.5 A |
| 3 mm | 5.3 A | 2.7 A | 8.8 A |
These are guide values calculated with the IPC-2221 formula for a single trace, not a guarantee. Neighbouring traces, an enclosed housing, an ambient temperature well above 25 °C and pulsed currents change the result. Keep a safety margin.
What changes the result
- Copper weight. Going from 35 to 70 µm raises the capacity by roughly 65 %.
- Inner layers. A buried trace sheds heat much worse than one on the surface: plan for about half of the outer-layer value.
- Accepted temperature rise. Allowing 20 °C instead of 10 °C adds about a third to the current.
- Voltage drop. Copper of 35 µm has about 0.5 mΩ per square. A trace 1 mm wide and 100 mm long is 100 squares, about 49 mΩ — at 2 A that is roughly 0.1 V lost.
What can be manufactured
Wide traces are never a problem; very narrow ones are limited by the etching process, and the limit depends on the copper thickness. The minimum trace and spacing at PCB-ELECTRA are 0.15 mm / 0.15 mm on 18 µm base copper (up to 35 µm final), and grow with the copper weight: 0.22 mm / 0.22 mm on 35 µm base copper and 0.28 mm / 0.28 mm on 70 µm. See the exact table under capabilities and the background on copper in our copper thickness guide.
Practical advice
- For power paths use wide traces or copper pours, and 70 µm copper if the width is limited.
- Carry high current between layers with several vias in parallel, never with a single one.
- Prefer rounded or 45° corners to sharp 90° corners.
- Widen inner-layer traces compared with outer ones for the same current.
- Check clearances for the voltage that will be present, not only the manufacturing minimum.
Configure your board in the price calculator, or contact us if the design carries high currents and you want a second opinion.
Frequently asked questions
What is the smallest trace width and spacing you manufacture?
On 18 µm base copper, 0.15 mm trace and 0.15 mm spacing. With thicker copper the limits grow: 0.22 mm for 35 µm and 0.28 mm for 70 µm.
How wide must a trace be for a given current?
It depends on the copper thickness, on whether the trace is on an outer layer, and on the temperature rise you accept. Use the IPC-2221 formulas or a trace width calculator, and add a margin.
Are inner traces rated for less current than outer ones?
Yes, as a rule. Inner traces lose heat less easily than outer ones, so they need to be wider for the same current.
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