About the PCB Trace Width Calculator
How wide must a copper trace be to carry a given current without overheating? The IPC-2221 formula gives a good first answer. Enter the current, the temperature rise you allow, the copper weight and whether the trace is on an outer or inner layer. The calculator returns the minimum width in millimetres and mils, the copper thickness and the cross-section. If you also type a trace length, it shows the resistance, the voltage drop and the power lost as heat. It is meant for quick design checks and learning. Always add a margin and follow your board maker's rules.
Updated October 2026
How to use the PCB Trace Width Calculator
- 1Enter the current the trace must carry.
- 2Enter the temperature rise you allow, for example 10 degrees.
- 3Choose the copper weight, usually 1 oz.
- 4Choose outer or inner layer.
- 5Optionally enter the trace length to see resistance and voltage drop.
How the formula works
Remember also that copper gets hotter as it carries current, and its resistance rises with temperature, so a trace running at the limit is slightly worse than the cold resistance shows. Staying below the limit gives you room for this effect.
IPC-2221 relates the current to the cross-section area of copper: I equals k times the temperature rise to the 0.44 power times the area to the 0.725 power. The constant k is 0.048 for outer layers and 0.024 for inner layers. The calculator reverses this to find the area, then divides by the copper thickness to get the width.
The result is a minimum. Using a wider trace costs nothing on most boards and lowers the resistance, the voltage drop and the heat.
Practical tips
- Round the width up to the next convenient size.
- Short narrow necks, such as at a pad, are acceptable for a few millimetres.
- Use several vias in parallel to change layers, since a single via carries only a limited current.
- Check the fabricator's minimum width and spacing.
- For power above a few amps, a copper pour is often simpler than a long trace.
Related tools
Use the Voltage Drop Calculator to check a long cable run, the Wire Gauge Calculator to pick a wire size and the Wire Resistance Calculator for any conductor. The Ohm's Law Calculator gives quick checks of voltage, current and resistance, and the LED Resistor Calculator handles small parts. Always verify the design with your board house.
Features
- IPC-2221 formula for outer and inner layers
- Width in millimetres and mils
- 0.5, 1, 2 and 3 oz copper
- Resistance, voltage drop and heat for a length
- Sensible range checks
- Runs in your browser
Frequently asked questions
What is IPC-2221?
It is a standard for printed board design. Its charts and formulas give the current a trace can carry for a given temperature rise, and this tool uses its equation.
What temperature rise should I allow?
10 degrees is a common conservative choice. Allowing 20 or 30 degrees gives a narrower trace but runs hotter, which matters near sensitive parts.
Why are inner layers wider?
Inner traces cannot shed heat to the air as well as outer ones, so the formula needs about twice the area for the same current.
What does 1 oz copper mean?
It means copper weighing one ounce per square foot, which is about 35 micrometres thick. 2 oz is about 70 micrometres.
Is the result a safe design value?
It is a starting point. Real boards have vias, nearby heat sources and manufacturing tolerances, so add a margin and consider using wider traces or copper pours.
Does it work for high frequency or fast signals?
No. This is for DC or low frequency current capacity only. Impedance and skin effect are separate topics.
What about very large currents?
The formula is fitted up to roughly 35 amps. Above that use a copper pour, bus bars or a thicker design.