Calculate required PCB trace width for a given current using IPC-2221 standards. Find the minimum trace width for your copper weight and temperature rise limit.
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 tool 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.
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.
A = (I / (k × ΔT^0.44))^(1/0.725), where k=0.048 (external), k=0.024 (internal). Width = A / thickness. Thickness = oz × 1.37 mil. Results: width in mils, then converted to mm. Voltage drop = I × R, where R = ρ × L / A.
Result: 20.8 mil (0.53 mm) minimum trace width
For 2A on an external 1oz copper trace with 20°C rise: area = (2/(0.048×20^0.44))^(1/0.725) = 28.5 mil². Width = 28.5/1.37 = 20.8 mil.
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.
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.
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.
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.
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.
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.
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.
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.
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.