How to Calculate Joules?

Have you ever come across the word joules when reading a manual for an electrical product and wondered what it really was? Have you ever wanted to calculate joules but thought it was too difficult?

A joule is a unit of measurement that is important to so much of what we do in the modern world, but most of us don’t know anything about it. Not to worry, we are here to explain exactly what a joule is so you don’t have to be afraid of it anymore.

In science, the joule is the unit of energy or work. There are multiple ways to calculate joules. Read on how to calculate joules here.

In this article, we will walk you through how to calculate joules for the four most common uses: energy, electrical energy, kinetic energy, and work.

What Is a Joule?

A joule is an essential unit of measurement within the international metric system. The metric system also includes other important units of measurement, such as meters, kilometers, seconds, and amperes.

Most importantly: a joule is a unit of energy.

Joule Formulas

There are a number of very useful formulas for working out joules. Here is a quick reference list. We will go through each of them below.

  • Joules = watts x seconds
  • Joules = amps² x ohms x seconds
  • Joules = ½ x mass x (meters/seconds)²
  • Joules = newtons x meters

How to Calculate Joules?

There is no single formula for joule because energy comes in different forms. For example, it can be expressed as electricity, heat or work.

Instead, there are a number of different ways to calculate joules, depending on what you are using it for. Below, you will find the most common situations in which joules are used.

How to Calculate Energy in Joules


  • Energy = power x time
  • Joules = watts x seconds

This is the most basic formula for a joule. Basically, you can work out how many joules are being exerted by multiplying power by time.

A watt is a unit of power. You have probably seen it on light bulbs or electrical appliances you have bought. Joules are an important unit in working out the energy efficiency of these items.

This is because one watt is the amount of energy (joules) that is expended by the device each second. So, if you see a device like a lightbulb or washing machine that has a certain number of watts or kilowatts, you will know how much energy that device uses. You may consider working with an electrical services contractor if there’s electrical work that needs to be done with a specific amount of electrical energy. Since electrical work can be hazardous if performed incorrectly, consider hiring an electrician to complete the project for you. This will keep you safe and ensure the end result works as intended for a long time.

To learn more about how much energy your appliances use, you can take a look at this useful tool to convert kW to kJ.

How to Calculate Electrical Energy in Joules

  • Electrical energy = current² x resistance x time
  • Joules = amps² x ohms x seconds

Electrical energy is actually the same as the joule formula for energy in watts. This is because a watt is equal to (amps² x ohms).

An amp, also called an ampere, is a unit of electrical current. An ohm is a unit of electrical resistance. These units are particularly useful when manufacturing things like circuit boards.

Circuit boards use resistors to moderate the flow of electricity throughout a system. So the amount of energy expended by a circuit board in one second is just the square of the electrical current multiplied by the resistance within the circuit.

You can learn more about how circuits work here.

How to Calculate Kinetic Energy in Joules


  • Kinetic energy = ½ x mass x velocity²
  • Joules = ½ x kilograms x (meters/seconds)²

Kinetic energy is the amount of energy that an object possesses in motion. For example, if you drop a bowling ball off a building, the bowling ball possesses a certain amount of energy.

This is interesting because you can work out the equivalent amount of energy of a falling bowling ball to other types of energy, like a burning lightbulb.

The formula for kinetic energy in joules is pretty straightforward. You need to know the mass of the object, as well as the velocity at which it is traveling.

For example, you could work out the mass of a bowling ball and then drop it off a building to work out what its velocity is. To work out the velocity, you first work out how many meters it travels each second. Once you have that number, you square it, and then you get your velocity.

A bowling ball will accelerate when it is dropped off a building as it gathers momentum. Eventually, though, it will reach terminal velocity. Terminal velocity is just the maximum velocity that a falling object can reach.

Terminal velocity is a little bit complicated. But, as a quick reference, an object reaches terminal velocity when the drag force and buoyancy force of a falling object become equal to the force of gravity. You can learn more about terminal velocity here.

So, all you have to do is work each of those things out, and then you can compare the amount of energy your bedroom light uses and compare it to the amount of energy possessed by a falling bowling ball.

How to Calculate Work in Joules


  • Work = force x distance
  • Joules = newtons x meters

In physics, work is the amount of energy that is expended when a given force is exerted over a given distance. For example, you might want to find the amount of work produced by a weightlifter who lifts a certain amount of weight from the ground to above their head.

To work out the force of an object, you need to know what a newton is. A bit like terminal velocity, a newton is complicated.

Here is a short description: one newton is the amount of force that is used when one kilogram is accelerated at the rate of one meter per second squared.

Now You Have the Joules

Now you know exactly how to calculate joules. More importantly, now you can compare the amount of energy you exert in the gym to the amount of energy exerted by falling bowling balls and burning light bulbs!

For more interesting information and fun tips like this, have a look around our site!