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Every single device that involves the flow of electrical current is following the physical rules that are explained by Ohms Law. Using our Ohms Law calculator can help you solve for any variables in the equation.

But what is Ohms law? How do you use it? And how does this calculator work? Read this guide to learn more!


Why use an ohms law calculator?

Our Ohms law calculator will do all the heavy lifting for you.

Enter two known values of V, I or R and our handy calculator will solve the third one for you, instantly. It also calculates power for you at the same time.

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What is the formula for ohms law?

Ohms law sets out the rules that link these three values: V (voltage), I (current) and R (resistance). It is usually stated in the following form:

V = I * R

This means that the voltage is equal to the current multiplied by the resistance.

What are the variables in ohms law?

Ohms law is named after German Physicist Georg Ohm. He wrote a treatise on electrical currents passing through wires and created some equations that would eventually become Ohms law. But what does Ohms law actually relate to?


The first element of Ohms law is voltage, often abbreviated to the letter V. You will sometimes also see it signified by the letter E, which stands for electromotive force. Voltage is measured in units called volts.

Voltage is probably the most difficult to understand of the three components of Ohms law. In essence, it is a measurement of the strength of a power source to push electricity around a circuit.

The higher the voltage, the stronger the push. So for instance, a battery might have a voltage of 1.5 V. In comparison, a 3 V battery would have twice the strength to push electricity around the circuit.


Current is most easily described as the flow of electricity around a circuit. Current is measured in units called amperes, or amps. In Ohms law, it is represented by the letter I.

The larger the push from the power source (and therefore the larger the voltage) the more current will flow around the circuit. As you would imagine, if you double the amount of voltage, you will double the amount of current.


The final part of Ohms law is resistance. Resistance is measured in units called Ohms, named after (you guessed it) our friend Georg again. In Ohms law, resistance is represented by the letter R.

Resistance (not to be confused with resistivity) is basically a measurement of how hard it is to get current to flow around the circuit. It has a different value for different materials - the more easily current can flow through a material, the lower the resistance.

The length and thickness of a wire will also affect resistance. It is harder for the current to flow through a thin wire than a thick one.

What's an example of ohm's law?

There are three possible situations in which we would make use of Ohms law. We could use it to find the voltage, or the current, or the resistance.

Finding V

This is the simplest of the three since Ohms law is written with V as the subject.

As we saw before, V=IR means that voltage is current multiplied by resistance. So if we know the current and resistance, we just need to multiply them to find V. For example, if the resistance of the circuit is 10 ohms, and the current is 5 amps then:

V = I * R

V = 10 x 5

V = 50 Volts

This isn't too tricky. Finding I and R is a little more complicated.

Finding I

To find I, we need to rearrange the equation to make I the subject.

In the original equation V=IR, I is being multiplied by R. So to undo that, we need to divide both sides by R. This gives V/R=I. Putting I first it becomes I=V/R. We can now use this equation to find I. Using the same values as before, if the voltage is 50 volts and the resistance is 10 ohms, we can find I as follows:

I = V / R

I = 50 / 10

I = 5 amps

Finding R

We need to do a similar trick to make R the subject of the equation.

V=IR has R being multiplied by I. So if we divide both sides by I, we get V/I=R. Putting R first, it becomes R=V/I. Using the same values as in the previous examples, if V is 50 volts and I is 5 amps, we can calculate R as follows:

R = V / I

R = 50 / 5

R = 10 ohms

How is ohms law used in real life?

It's the question that is dreaded by every math teacher on the planet: yeah, but when am I ever going to need this in real life?

Well, millions of people who work with electrical circuits in their day-to-day lives and jobs will need to use Ohms law. But you may be surprised to know that if you're one of the nearly 40 million smokers in the US, you might need to use it too.

A big part of the vaping scene is something known as sub ohm vaping. This involves modifying vaping equipment so that the resistance is below one ohm. Ohms law tells us that if you reduce the resistance you increase the current. More current means more power which leads to bigger vaping clouds.

As you can see, you never know when you might need to make use of Ohms law.

We also have a whole host of other calculators to meet your every calculating need. From those complex business calculations to every type of conversion you could ever think of, we're here to make your life a little bit easier.

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