PCB Trace Width Calculator

PCB Trace Width Calculator estimates the copper width required for a target current and temperature rise, or calculates approximate current capacity from an existing trace width.

PCB Trace Width Calculator formulas

The empirical current equation uses cross-sectional area in square mils, current in amperes and temperature rise in degrees Celsius. One ounce of finished copper is approximated as 1.378 mil, or about 35 micrometers, before fabrication tolerance and plating are considered.

Worked example

For 2 A on an external layer, 1 oz copper and a 10°C allowable rise, the legacy equation gives a minimum trace width close to 30 mil, or about 0.76 mm. A 100 mm trace at that width has an estimated resistance near 0.065 Ω at 20°C, producing roughly 0.13 V drop and 0.26 W loss. The calculator also shows a width with 25 percent design margin.

Designing practical PCB conductors

The PCB Trace Width Calculator is a planning tool because trace width is only one part of current-carrying performance. Copper thickness, board stack-up, nearby planes, airflow, solder mask, ambient temperature, duty cycle and adjacent heat sources all affect temperature. A short external trace connected to large copper areas may cool better than a long internal trace surrounded by insulating laminate.

External and internal layers

The older IPC-2221 relationship assigns a lower constant to internal traces, producing a wider requirement for the same current and allowed rise. Modern IPC-2152 methods use test data and correction factors that better represent board construction. Use the result as an early estimate, then verify the design with appropriate standards and thermal analysis.

Copper weight and finished thickness

Nominal copper weight is often quoted in ounces per square foot. One-ounce copper begins near 35 µm, but etching, plating and fabrication tolerances affect finished geometry. Ask the fabricator about minimum width, spacing and finished copper thickness, particularly for heavy-copper boards or controlled-impedance designs.

Voltage drop and power loss

The PCB Trace Width Calculator highlights that narrow traces have higher resistance, voltage drop and I²R heating. The resistance estimate uses room-temperature copper resistivity; copper resistance rises as it heats. Sensitive low-voltage circuits may therefore require a wider trace than the thermal calculation alone suggests. High-current paths also need attention at vias, pads, connectors, neck-down regions and layer transitions.

Use a design margin

The PCB Trace Width Calculator reports a 25-percent width margin because calculated minimums should not be treated as manufacturing targets. Increase margin for uncertain loads, continuous duty, high ambient temperature or limited airflow. Parallel copper pours, multiple traces or additional layers can reduce resistance, but current sharing and via capacity still require analysis.

For production work, consult the applicable IPC-2221B standard overview, IPC-2152 guidance, component specifications and your PCB manufacturer. Validate high-current or safety-related boards by measurement under worst-case operating conditions.

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Frequently asked questions