This Javascript web calculator calculates the trace width for printed circuit board conductors for a given current using formulas from IPC2221 (formerly IPCD275).
Inputs:
Current  Amps  
Thickness 
Optional Inputs:
Temperature Rise  Deg  
Ambient Temperature  Deg  
Trace Length 
Results for Internal Layers:
Required Trace Width  
Resistance  Ohms  
Voltage Drop  Volts  
Power Loss  Watts 
Results for External Layers in Air:
Required Trace Width  
Resistance  Ohms  
Voltage Drop  Volts  
Power Loss  Watts 
Notes:
The trace width is calculated as follows:
First, the Area is calculated:
Area[mils^2] = (Current[Amps]/(k*(Temp_Rise[deg. C])^b))^(1/c)
Then, the Width is calculated:
Width[mils] = Area[mils^2]/(Thickness[oz]*1.378[mils/oz])
For IPC2221 internal layers: k = 0.024, b = 0.44, c = 0.725
For IPC2221 external layers: k = 0.048, b = 0.44, c = 0.725
where k, b, and c are constants resulting from curve fitting to the IPC2221 curves
Disclaimer:
These calculations are believed to be correct, but not guaranteed. Use at your own risk! 

Trace Width Calculator FAQs  
QUESTION: Very cool PCB width tool! I would like to know its limits though. I entered a 65 amp
current requirement and it returned a track width that must be incorrect.
ANSWER: The original graphs that this tool is based on (published in IPC2221) only cover up to 35 Amps, up to 0.4 inches of trace width, from 10 to 100 degrees C of temperature rise, and copper of 0.5 to 3 ounces per square foot. The formulas used here will simply extrapolate when the values are outside of these ranges. QUESTION: I used your PCB trace width calculator. Intuitively I would say the required internal trace width would be less than the external case since the external trace can peal off; the opposite is true according to the calculator???? Why? ANSWER: In air, the external layers have better heat transfer due to convection. A good heat insulator blankets the internal layers, so they get hotter for a given width and current. Since the Trace Width Calculator tries to control the temperature rise of the traces, it makes the internal traces wider. In vacuum, or in a potted assembly, you should use the internal layer guidelines even for the external layers. QUESTION: What does temperature rise mean and how does it apply? ANSWER: Temperature rise means how much hotter the trace will get with current flowing in it compared to without. You have to decide how much temperature rise your board can handle based on the operating environment and the type of PWB material used. Ten degrees is a very safe number to use for just about any application. If you can live with the trace width required for a tendegree rise, you are good to go. If you want to try to skinny up the traces, ask for 20 degrees of temperature or more. QUESTION: I use "wagon wheels" or "spokes" when connecting to a ground plane to make it easier to solder to. The trace width calculator is telling me to make the "spokes" so wide that it defeats the purpose. What should I do? ANSWER: The wagon wheels spokes are very short length traces and are heat sunk to the plane. The trace width calculator uses empirical formulas based on long traces with no special heat sinking. Generally, the wagon wheel spokes do not have to be anywhere near as wide as long traces. However, at this time, I don't know of a good way to do calculations for wagon wheel spokes. QUESTION: What are Mils? ANSWER: A Mil is 1/1000 of an inch. 

This calculator is hosted for 4pcb.com by circuitcalculator.com Email questions or comments about this calculator to: © Copyright 2007 Brad Suppanz. All rights reserved. 