PCB Trace Width Calculator

Size internal or external PCB copper traces for current, copper weight, and allowable temperature rise using the IPC-2221 equation.

Estimate the minimum conductor width and cross-sectional area for an early PCB power-routing check.

Enter the design current, temperature rise, copper weight, and layer location.

Trace Location

Current (A)

Allowable Temperature Rise (°C)

Copper Weight (oz/ft²)

About PCB trace width calculations

PCB trace width determines how much current a copper conductor can carry without an excessive temperature rise. Current flowing through finite resistance creates heat, and a narrow trace has less cross-sectional area to conduct electricity and spread that heat. This calculator rearranges the empirical IPC-2221 current equation to estimate the minimum area and width required for a chosen current, copper weight, temperature rise, and layer position. The equation is I = k × ΔT^0.44 × A^0.725, where current I is measured in amperes, allowable temperature rise ΔT is in degrees Celsius, and cross-sectional area A is in square mils. The coefficient k is 0.048 for an external trace and 0.024 for an internal trace. Internal conductors are surrounded by laminate and generally dissipate heat less effectively, so the older IPC model assigns them a larger required area. After solving for area, the calculator divides by copper thickness. One-ounce copper is approximately 1.378 mils, or 35 µm, thick before fabrication tolerances. Two-ounce copper doubles nominal thickness and therefore needs roughly half the width for the same cross-sectional area. Finished thickness can be changed by plating and process variation, so obtain the actual stackup from the PCB fabricator for critical designs. Temperature rise means the trace temperature above its local ambient condition, not the maximum ambient itself. A 10°C rise is conservative and common for sensitive or high-reliability circuits. Allowing 20°C or 30°C produces a smaller trace, but it also raises conductor resistance, warms nearby components, and reduces margin during overloads. Consider the enclosure temperature, copper planes, airflow, duty cycle, and neighboring hot parts. IPC-2221 is a useful preliminary sizing model rather than a complete thermal simulation. Modern IPC-2152 guidance includes board construction and environmental effects in more detail. Pads, vias, connectors, neck-downs, solder mask, parallel planes, and short transient currents can all change real performance. Round the answer upward to a manufacturable width, add engineering margin, verify voltage drop separately, and test high-current prototypes under worst-case operating conditions before releasing a design.

PCB trace width examples

Representative copper-trace results from the IPC-2221 model.

Design condition	Minimum width	Interpretation
External, 1 A, 10°C rise, 1 oz	11.83 mil / 0.300 mm	A modest outer-layer supply trace.
Internal, 2 A, 20°C rise, 1 oz	52.55 mil / 1.335 mm	Internal routing requires substantially more width.
External, 5 A, 20°C rise, 2 oz	35.74 mil / 0.908 mm	Heavier copper reduces the required width.

How to size a PCB trace

Choose whether the conductor is on an external or internal copper layer.
Enter the maximum continuous current and acceptable temperature rise.
Enter the finished copper weight from the board stackup.
Click Calculate, then round the minimum width upward and add design margin.

PCB trace width FAQ

What temperature rise should I choose?

Ten degrees Celsius is a conservative starting point, while 20°C is common in general commercial designs. Use a lower rise when nearby parts are temperature-sensitive or reliability requirements are strict.

Why are internal traces wider?

Internal copper is enclosed by laminate and cannot transfer heat to ambient air as directly. The IPC-2221 coefficient reflects this reduced heat dissipation.

Does two-ounce copper halve the required width?

For the same calculated area, doubling nominal thickness approximately halves width. Fabrication limits and finished copper thickness can prevent the relationship from being exact in production.

Is IPC-2221 the newest sizing method?

IPC-2152 provides more detailed thermal guidance and is preferred for rigorous work. IPC-2221 remains useful for quick, conservative early estimates.

Should I use the exact calculated width?

No, round upward to a practical routing width and include manufacturing and operating margin. Confirm voltage drop and prototype temperature under worst-case conditions.