Electrician Math: Life-Saving Skills

Electrician math is vital to your career, maybe even your life.

When you construct a building that will last, you have to start with a strong foundation.

No one sees the foundation when the building is finished, but it is an essential part of the structure. Electrical formulas and concepts are the foundation you need to be a successful electrician.

Many people don’t even realize how important math is in their lives. You use it in just about everything you do. From measuring the coffee grounds and water for your coffee in the morning to counting your money at the grocery store – everything involves math in some shape or form.

This is especially true for an electrician. You are constantly calculating measurements and voltages. You will always be using basic arithmetic (mostly fractions) to calculate many of these measurements.

You will need to know basic right angle trigonometry when bending conduit, in order to find the correct angle and the necessary distance between bending points. Just about every job you do will involve some type of math.

As you study electrical circuits, you will find that a solid foundation in math will help you understand the NEC and its provisions.

The electrician math unit you will study, as part of the classroom training you need to complete your electrician’s apprenticeship, includes electrical fundamentals and an explanation of how electrical meters work in order to help you visualize how they are used in practice.

As you continue with your electrical studies, you will be amazed at how often the basics you learned in your math unit will return. Ohm’s law and the related electrical formulas are the foundation of all electrical circuits.

Changing a Fraction to a Decimal

Students grasp ideas and concepts at different rates. You may find parts of your math unit as a simple review of what you already know, or you may find you need a great deal of concentration to fully understand some things.

Either way, make certain you do fully understand each concept before moving on to the next. This way you will build a solid foundation that will help you throughout your career.

To change a fraction into a decimal, divide the top number (numerator) by the bottom number (denominator).

For example:

1/6 = 1 divided by 6 = 0.166


Values are often displayed as percentages. One hundred percent is equal to the entire value, 50 percent is half, and 25 percent is a quarter of the total value.

Multiplying or dividing a percentage is easier when you first convert the value into a decimal and use the new number in your calculation.

To change a percentage to a decimal, drop the % and move the decimal 2 place to the left.

For example:

45.2% = 0.452


If you need to change a number by multiplying it by a percentage, the percentage is called the multiplier.

First you must convert the percentage into a decimal, and then multiply the number by the converted decimal value.

For example:

An over current protection device, such as a fuse or a circuit breaker, must be sized no less than 125% of the continuous load.

For a load that is 80A, the over current protection device can not be sized less than 100A.

To get this answer, we convert 125% to 1.25 and multiply 80 x 1.25 = 100A 

The maximum continuous load on a circuit breaker is limited to 80% of the device rating.

For a device rated at 50A, what would be the maximum continuous load permitted? 40A.


80% = 0.80
Multiply 0.80 x 50A = 40A

More Electrician Math

These are just a few examples of the types of calculations you will encounter in electrician math. As the course progresses, the calculations will get more complicated.

For example, you will learn how to increase a number by a specific percentage – you may come across a need for this calculation if the feeder demand load for a range needs to be increased by a certain percent.

You will also learn all types of formulas involving ohms and watts. For example, you may need to know how much power is consumed in watts by a 12 AWG conductor, 200 feet long with a total resistance of 0.40 ohms, if the current in the circuit is 16A.

The formula for this problem is Power = I2 x R 

P = I2 x R
I = 16A
R = 0.40 ohms
P = 16A2 x 0.40 ohms
P = 16A x 16A x 0.40 ohms
P = 102.40W

Answers can be rounded to the nearest 50, so the correct answer is 100W.

Build a strong foundation and your life as an electrician will be much easier. Keep in mind that a strong foundation begins with a solid understanding of electrician math.

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Industrial Electrician Dusten Huebner
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