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AWG and Circular Mils

David A. Snyder, P.E.

Course Outline

This 3 PDH course discusses the concepts of AWG sizes, circular mils, KCMIL, Class B conductor stranding, and skin effect or depth of penetration.  In order to double-check the equations and results presented in the course write-up, a calculator that can perform ex, x√y, and yx is required, but a simple non-scientific calculator with square-root is all that is required for the quiz at the end of the course.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

The following learning objectives are included in this course:

Intended Audience

Anyone who is involved in the specification, design, or installation of electrical wiring will benefit from this course.

Benefit for Attendee

Upon successful completion of the course, the reader will have a thorough understanding of AWG, circular mil, and KCMIL wire size conventions for stranded and solid conductors.

Course Introduction

Conductors, also known as wires, cables, or busses, conduct electricity from one point to another. This course discusses the difference between solid and stranded conductors, and the size conventions (circular mils. KCMIL, and AWG) used to describe them. As the names would imply, solid conductors are composed of one solid piece of wire, whereas stranded conductors are composed of several smaller strands of solid wire. The terms circular mils, KCMIL, and AWG (American Wire Gage) are not quite as obvious and often require further explanation. The concept of skin effect or depth of penetration will also be discussed for AC power and signals.

Course Content

The course content and tables are in the following PDF files:

AWG and Circular Mils

AWG and Circular Mils - Tables

Please click on the above underlined hypertext to view, download or print the document for your study. Because of the file size, we recommend that you first save the file to your computer by right-clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader from your computer.

Course Summary

This course takes an in-depth look at several concepts that are taken for granted by many but understood by few.  The concept of circular mils isn’t obvious to everyone, but it is presented in simple terms in this course.  The AWG numbered sizes are all related to each other by a simple mathematical function that is explained in detail in this course with many examples and illustrations.  The KCMIL sizes are not related to the AWG numbered sizes by the same mathematical formula but are designated by their cross-sectional area.  Many examples are given to explain the quantity and sizing of the strands of stranded conductors.  The phenomenon of skin effect or depth of penetration is also discussed.


Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

Take a Quiz

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.