How Basic Electrical Math Works

You don’t have to be the next Albert Einstein to understand electrical math. In fact, many people are surprised by how easy electrical math can be – especially when just looking at the basics. Today, that’s exactly what we’re going to teach you.

Understanding Watts (Power)

In order to understand electrical math, you first need to understand how Watts work. But don’t worry: if you understood current and voltage in our last lesson, then understanding Watts will be a piece of cake.

The Watt is a measure of power, better understood as how much energy is released per second. Watts are generally shortened to W. We can easily determine the Wattage of anything by multiplying voltage (V) by current (amps, written as I):

W = V x I

If a current of 2A is flowing through a bulb with 12V across, then it would generate 24W of power.

You can always calculate wattage if you know 2 of the following three variables:




The best way to understand how these formulas are related is by using a simple circle:

At first glance, that circle looks complicated and intimidating. But don’t worry. Once you understand how to read the circle, you’ll realize how valuable it is at calculating all aspects of electricity.

Let’s say you need to calculate power. Look at the top left corner of the circle. Find the two variables that you know (either V and I, V and R, or I and R) then follow the formula listed. So if you need to calculate power and only have I and R, then you could do that by using the formula:

I2xR = Power

Putting electrical math into practice

In the United States, domestic power is supplied at 110V. In Europe, Australia, Asia, Africa, and other parts of the world, domestic power is generally supplied at between 220V and 240V.

In the United States, a 100W lightbulb connected to a standard power outlet will draw a current of 100/110 Amps (about 0.9A). To understand how we got that number, simply look at the circle above, find Amps (I = Current) and then plug the two numbers we know into the formula given:

P/V = I

Once you know the voltage of the power supply you’re working with as well as the wattage of the bulb, fuse, or electrical appliance, then you can always calculate the current flowing through that device.

Now that you know how to use the power circle formula chart listed above, you can calculate all of the basics of electricity. As long as you have two of the three variables, you can always calculate the third or fourth variables using the formulas listed in that circle.

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