PCB Trace Width Calculator

About the PCB Trace Width Calculator

The PCB Trace Width Calculator determines the minimum trace width needed to carry a specified current based on IPC-2221 standards. This is the inverse of the current capacity calculator — you specify how much current you need to carry, and the tool tells you how wide the trace must be.

Properly sizing traces is one of the most important aspects of PCB design. Traces that are too narrow will overheat, potentially causing solder joint failure, delamination, or fire. Traces that are wider than necessary waste board space and can complicate routing. This calculator finds the optimal width for your requirements.

The calculator supports all standard copper weights, both internal and external layers, and provides results in both mils and millimeters. It includes a comprehensive trace width table showing widths for various currents and temperature rises, making it easy to build a complete power distribution design. The tool also shows voltage drop and resistance for the calculated trace width at a given length.

When This Page Helps

Use this calculator when you know the current requirement and need a practical minimum trace width before routing a board. It helps you size power traces with enough thermal margin without wasting board area everywhere else. That is especially useful when you are balancing routing constraints against heat and voltage-drop limits.

How to Use the Inputs

1. Enter the required current in amperes
2. Select the copper weight for your PCB stackup (1oz standard, 2oz for power)
3. Choose internal or external layer — external can be narrower for the same current
4. Set the maximum allowable temperature rise above ambient
5. View the minimum required trace width in mils and millimeters
6. Optionally enter trace length to see voltage drop at that width

Example Calculation

Tips & Best Practices

• Always round up to the next standard trace width (5, 6, 8, 10, 12, 15, 20, 25, 30, 40, 50 mil)
• For high-current paths, consider using copper pours instead of traces — much lower resistance
• Internal traces need roughly twice the width of external traces for the same current
• When routing through tight areas (BGA escape), use heavier copper to maintain current capacity with narrower traces
• Verify voltage drop across the entire power path, not just the narrowest section

Trace Width Selection Guide

For most digital designs, signal traces use 5-8 mil widths (adequate for milliamp-level signals). Power traces typically need 15-50 mil depending on current. For motor drivers, battery chargers, and power supplies carrying 5A+, consider 50-100 mil traces or copper pours. Always verify both current capacity and voltage drop — for long traces, voltage drop often dictates a wider trace than current alone would require.

Manufacturing Considerations

PCB manufacturers etch traces from copper foil, and the etching process affects final trace width. Over-etching narrows traces (common), while under-etching widens them. Typical tolerance is ±1-2 mil for standard processes. For critical power traces, specify minimum width after etching in your fabrication notes, and ask the fab to adjust artwork compensation accordingly.

Multi-Layer Power Distribution Strategy

Modern PCBs distribute power across multiple layers. A common 4-layer stackup uses Layer 2 as a ground plane and Layer 3 as a power plane, with signal/power traces on Layers 1 and 4. Power planes provide extremely low resistance and serve as decoupling capacitors with the ground plane. For complex power trees, consider dedicated power layers with split planes for different voltage rails.

Frequently Asked Questions

• What trace width do I need for 1A?

  For 1oz external copper with 20°C rise: about 10 mil (0.25mm). For internal: about 23 mil (0.58mm). These are minimums—always add margin for manufacturing tolerance.

• Should I use the minimum calculated width?

  Add at least 20-50% margin above the minimum. Manufacturing tolerances, plating variations, and proximity to other heat sources can reduce effective current capacity. Round up to the next standard width.

• What is the minimum trace width my fab can produce?

  Standard PCB fabrication supports 5-6 mil minimum trace width. Advanced fabs can do 3-4 mil. HDI boards with laser-drilled vias can achieve 2.5-3 mil. Check with your manufacturer for capabilities and cost impact.

• How does 2oz copper compare to 1oz?

  Doubling copper weight halves the required trace width for the same current capacity. A 20 mil trace in 1oz copper carries the same current as a 10 mil trace in 2oz copper. However, 2oz copper costs more and limits minimum trace spacing.

• Do I need controlled impedance for power traces?

  Power traces don't need controlled impedance since they carry DC or low-frequency current. Size them purely for current capacity and voltage drop. Only signal traces carrying high-frequency data need impedance control.

• Can I use polygon/copper pour instead of traces?

  Yes — copper pours are excellent for power distribution. They provide massive cross-sectional area, low resistance, and good thermal spreading. Use pours for power and ground whenever routing space allows.