PCB Trace Width
Calculate the required PCB trace width for a given current using IPC-2221. Get trace width in mils and mm, cross-section area, resistance, and voltage drop.
Additional Inputs
About This Calculator
The PCB Trace Width Calculator helps electronics engineers, PCB designers, and hobbyists determine the minimum required width of copper traces on a printed circuit board using the industry-standard IPC-2221 (formerly IPC-D-275) formula. Proper trace width design prevents overheating, voltage drops, and circuit failures while optimizing board space and copper usage.
The calculator uses the IPC-2221 empirical formula: cross-section area A = (I / (k × Trise0.44))1/0.725, where k = 0.048 for external traces and 0.024 for internal traces. The trace width is then calculated as W = A / (1.378 × t), where t is the copper thickness in oz/ft². Results are provided in both mils (thousandths of an inch) and millimetres. When you provide the trace length, the calculator also computes the DC resistance using copper's resistivity (1.724 × 10⁻⁶ Ω·cm at 20°C) with temperature compensation (0.39%/°C), along with the voltage drop and power dissipation.
This tool is essential for power electronics designs, LED lighting circuits, motor controllers, battery management systems, and any application where PCB traces must carry significant current without exceeding temperature limits. The formula applies to DC and low-frequency AC signals; for RF applications, additional considerations such as skin effect and impedance matching are required.
Regional Notes
Global: The IPC-2221 standard is universally adopted by the electronics industry worldwide. Copper thickness is universally measured in oz/ft², a standard inherited from the US customary system but used globally in PCB fabrication. Trace width results are provided in both mils (common in US-based fab houses) and millimetres (common in European and Asian fab houses). Always verify your chosen PCB manufacturer's minimum trace width and spacing capabilities before finalizing your design.
Frequently Asked Questions
What is the IPC-2221 standard for PCB trace width?
IPC-2221 is the industry standard for designing PCB traces. It provides formulas to calculate the required trace width based on current, copper thickness, temperature rise, and whether the trace is on an internal or external layer. External traces can carry more current for the same width because they dissipate heat better.
How do I calculate PCB trace width?
Using the IPC-2221 formula: cross-section area A = (I / (k × Trise^0.44))^(1/0.725), where k = 0.048 for external traces and 0.024 for internal traces. Then width in mils = A / (1.378 × thickness in oz/ft²). Enter your current, copper thickness, and temperature rise to get the minimum required trace width.
What is the difference between internal and external PCB traces?
External traces are on the outer layers of a PCB and can dissipate heat directly into the air, allowing them to carry more current for the same width. Internal traces are embedded within the PCB substrate and have poorer heat dissipation, so they need to be wider for the same current and temperature rise.
What copper thicknesses are commonly used on PCBs?
Standard PCB copper thickness is 1 oz/ft² (35 µm), with 2 oz/ft² (70 µm) used for higher current applications. Thicknesses of 0.5 oz/ft² (17.5 µm) are used for fine-pitch designs, and 3 oz/ft² (105 µm) or more for power electronics requiring very high current capacity.
How does temperature rise affect PCB trace width?
Higher temperature rise allows narrower traces for the same current because the formula accounts for the increased heat dissipation at higher temperatures. However, PCB materials typically have a maximum operating temperature around 130-180°C, so the trace temperature (ambient + rise) should stay within safe limits.
What is the resistance of a PCB trace?
PCB trace resistance depends on the cross-section area, length, and copper resistivity (1.724 × 10⁻⁶ Ω·cm at 20°C). Resistance increases with temperature at a rate of 0.39% per °C. Enter the trace length to calculate resistance, voltage drop, and power dissipation.
Can I use this calculator for high-frequency PCB traces?
This calculator uses the DC IPC-2221 standard which is suitable for DC and low-frequency applications. For high-frequency traces (above 100 MHz), additional factors like skin effect, impedance matching, and dielectric losses become significant and require specialized RF design tools.
What safety margin should I add to the calculated trace width?
It is recommended to add at least 10-20% safety margin to the calculated trace width to account for manufacturing tolerances, etching variations, and unexpected current spikes. For critical applications like power supplies or safety circuits, consider using 25-50% wider traces.