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PCB trace width calculator (IPC-2221)

Size a printed-circuit-board trace for a given current using the IPC-2221 standard. Enter the current, the allowed temperature rise, the copper weight and whether the trace is external or internal, and it returns the required width in mils and millimetres — plus resistance and voltage drop if you give a length.

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Enter Current, Allowed temperature rise, Copper weight (oz/ft²), Trace location, Trace length (mm, optional) and the PCB trace width calculator (IPC-2221) works out Required trace width, Required trace width, Cross-sectional area, Trace resistance (if length given), Voltage drop, Power dissipated straight away.

How to use it

  1. Enter your values: Current, Allowed temperature rise, Copper weight (oz/ft²), Trace location, Trace length (mm, optional).
  2. Read the result instantly: Required trace width, Required trace width, Cross-sectional area, Trace resistance (if length given), Voltage drop, Power dissipated.

Frequently asked questions

What does the PCB trace width calculator (IPC-2221) actually compute?

It takes Current, Allowed temperature rise, Copper weight (oz/ft²), Trace location and Trace length (mm, optional) and derives Required trace width, Required trace width, Cross-sectional area, Trace resistance (if length given), Voltage drop and Power dissipated from them. The calculation is live as you type, so the result updates on every change.

What information do I need to provide?

5 values: Current (A), Allowed temperature rise (°C), Copper weight (oz/ft²), Trace location and Trace length (mm, optional). Nothing else is required — no account, no file upload.

Which “Copper weight (oz/ft²)” option should I choose?

You can pick between « 0.5 oz (17 µm) », « 1 oz (35 µm) », « 2 oz (70 µm) », « 3 oz (105 µm) » and « 4 oz (140 µm) ». Each one changes what the calculator works out, so switch and compare — the default is « 0.5 oz (17 µm) ».

Which units should I enter the values in?

Enter Current A and Allowed temperature rise °C. Metric and US units are both supported — switch system and the figures convert for you.

When would I actually use this?

At the bench: sizing a resistor for an LED, reading a colour band, working out a divider ratio, and checking a part will not cook.

What is the most common mistake?

Choosing a resistance and forgetting the power rating. A value that is electrically right will still burn if the package cannot dissipate what passes through it — check the watts as well as the ohms.

How accurate is it, and what are the limits?

IPC-2221: A = (I/(k·ΔT^0.44))^(1/0.725) with k = 0.048 external / 0.024 internal, then width = A / (1.378·oz). Conservative and derived from the standard's charts — add margin for vias, connectors, high-density boards and safety. Resistance uses copper resistivity 1.72×10⁻⁸ Ω·m.

What is the difference between the PCB trace width calculator (IPC-2221) and the Inductive reactance calculator?

This one returns Required trace width and Required trace width; the Inductive reactance calculator returns Inductive reactance XL and Frequency. That is the whole difference — open the one whose figure you need.

Is there a tool for the next step?

555 timer calculator (astable & monostable) is the closest one after this: Design a 555 timer circuit in either mode. In astable mode, R1, R2 and C set the output frequency, high and low times and duty cycle; in monostable mode, R1 and C set the one-shot pulse width. The classic hobbyist chip, sized in seconds.

What else is worth having open alongside it?

Impedance calculator (RLC) and LED resistor calculator — they come up in the same task often enough to be worth a second tab.

Further reading

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