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## PCB Trace Width Calculator

This Javascript web calculator calculates the trace width for printed circuit boards.

Inputs:

 Current Amps Thickness oz/ft^2milmmum

Optional Inputs:

 Temperature Rise DegCF Ambient Temperature DegCF Trace Length inchfeetmilmmumcmm

Results for Internal Layers:

 Required Trace Width milmmum Resistance Ohms Voltage Drop Volts Power Loss Watts

Results for External Layers in Air:

 Required Trace Width milmmum 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 IPC-2221 internal layers: k = 0.024, b = 0.44, c = 0.725

For IPC-2221 external layers: k = 0.048, b = 0.44, c = 0.725

Trace Width Calculator FAQs

I used your PCB trace width calculator. Intuitively I would say the required internal trace width would be less than the external case . the opposite is true according to the calculator???? Why?

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, you should use the internal layer guidelines even for the external layers.

What does temperature rise mean and how does it apply?

Temperature rise means how much hotter the trace . 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 want to try to skinny up the traces, ask for 20 degrees of temperature or more.

What are Mils?

A Mil is 1/1000 of an inch.