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PCB Trace Width Calculator (IPC-2221)

Minimum copper trace width for a given current + temperature rise, per IPC-2221. Supports internal and external layers, 0.5–3 oz copper.

A
°C
oz
Result
0.300 mm (11.8 mil)
1 A · 10 °C rise · 1 oz · external
Width (mm)
0.300 mm
Width (mils)
11.83 mil
Cross-section
16.3 mil²
0.30 mm trace for 1 A — route a board that enforces this →
Method & assumptions

IPC-2221 §6.2 external conductor formula: Area(mils²) = ( I / (k · ΔT0.44) )1/0.725, Width = Area / (thickness × 1.378).

k = 0.048 for external layers (top/bottom, air-cooled),k = 0.024 for internal layers (heat-trapped). Valid range: 0.5–3 oz copper, ΔT 10–100 °C, I ≤ 35 A. Outside this range the formula still returns a number but should be treated as approximate.

What is a trace on a PCB?

A trace is a copper conductor etched onto the PCB substrate that carries current between components. Trace width determines two things: current-carrying capacity (via ohmic heating) and characteristic impedance (for high-speed signals). This calculator handles the current side.

How does copper weight affect trace width?

Copper weight (½ oz, 1 oz, 2 oz) is the mass of copper per square foot, which corresponds to thickness (0.017 mm, 0.035 mm, 0.070 mm). Thicker copper means more cross-section for the same trace width, so you can carry more current in a narrower trace. 2 oz copper cuts required width roughly in half compared to 1 oz.

External vs internal layer

External layers dissipate heat to the surrounding air; internal layers are surrounded by FR4 dielectric and trap heat. IPC-2221 accounts for this with the k constant — internal traces need roughly 1.4× the width of external traces to carry the same current at the same temperature rise.

Frequently asked

What is a trace on a PCB?
A trace is a copper conductor on the PCB that connects components. Its width determines both current capacity and impedance.
How wide should PCB traces be?
For 1 A at 10 °C rise on 1 oz external copper, IPC-2221 gives roughly 0.30 mm (12 mil). Scale up for higher current or lower temperature rise.
What is IPC-2221?
IPC-2221 is the generic standard for printed board design. Section 6.2 gives the trace-width vs current formulas this calculator uses.
Does trace width matter for signal traces?
For DC or low-frequency signals, only current-carrying capacity matters. For high-speed signals (>10 MHz edge rates), trace width also determines impedance — see the microstrip/stripline calculators.
Next step

When PCBEditor routes a board, power nets are drawn wider than signal nets, so you are not widening every supply trace by hand.

Route a board that enforces this width automatically →
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