The next time you’re digging into your bike’s electrical system to measure voltage, resistance, or current, it will help to know a little bit about Ohm’s Law.

In this blog post, you’ll discover:

  • What Ohm’s law is and the formula 
  • 4 examples of how to use Ohm’s Law to calculate everything from voltage to wattage

H2: What is Ohm’s Law?

In 1826, the German physicist Georg Ohm discovered s a special relationship between voltage, current, and resistance.

He discovered that if one of these electrical units changed, the change also affected the other ones.

For example, if the resistance increased, the current decreased.

This unique relationship between voltage, current, and resistance formed what is now known as “Ohm’s Law.”

So now that we know what it is let’s look at the formula itself.

Ohm’s Law formula

The easiest way to summarize Ohm’s law is by putting it into a triangle, like this one:

image of ohm's law formula

With the help of this triangle, you can calculate the voltage, current, resistance, or wattage – just by dividing or multiplying the value of two other units.

Let’s put this into context by taking a look at 4 examples.

In Practice – Calculating Voltage

You can determine the voltage by multiplying the electrical current by the resistance.

Since we don’t know the voltage, cover up the letter “U” in the triangle:

That leaves us with the letters “I” (current) and “R” (resistance).

And since they’re aligned horizontally, we’ll multiply them together to get the voltage.

Therefore, if a circuit has a current of 6 amperes, and a resistance of 2 ohms, the voltage is 12 V, since:


In Practice – Calculating Current

Let’s return to our triangle – this time, we’ll cover up the letter “I” (for current):

That leaves the letters “U” (voltage) and “R” (resistance). Also, notice that the “U” is located above the “R?”

That means that we’ll divide the voltage by the resistance to get the current.

If we have a circuit with a voltage of 12 volts and a resistance of 4 ohms, the current is equal to 3, since:


In Practice – Calculating Resistance

Once again, let’s go back to your Ohm’s Law triangle – this time, we’ll cover up the “R” for “resistance.”

And just like when we calculated the current, the two remaining letters are positioned above each other.

In other words – to determine the resistance, we’ll divide the remaining letters by each other.

A 12-volt circuit with a current of 3 amperes will therefore have a resistance of 4 ohms, since:


In Practice – Calculating Wattage

Finally, let’s use Ohm’s Law to determine Wattage – i.e., the amount of electrical power.

To determine the Wattage, we’ll multiply the voltage by the current.

For example, an 11-volt circuit with a current of 280 generates 3080 W (or 3,08 kW).