Ohms Law Power Wheel: Understanding the Electrical Formula Wheel

Thomas Hawkins April 10, 2016

Last updated on October 22nd, 2026.

Ohm’s Law describes how voltage, current and resistance interact. Electricians use it to understand and calculate these electrical values.

You can use Ohm’s Law with basic math skills. The Ohm’s Law Wheel helps you choose the calculation.

How To Use The Ohm’s Law Formula Wheel

The diagram resembles a triangle. You can use it to find a circuit’s amperage without an ammeter.

Divide the circuit’s VOLTAGE by its RESISTANCE, as shown in the Ohm’s Law formula wheel.

The formula wheel uses three letters, each representing a value.

E or V = VOLTAGE (volts)

I= CURRENT (amps)

R= RESISTANCE (ohms)

Place your finger over the value you need to find, whether voltage, current or resistance. The formula wheel shows the calculation to use.

The Ohm’s law formula wheel is represented mathematically in three simple equations.

I (current) x R (resistance) = E (voltage)

E (voltage) ÷ R (resistance) = I (current)

E (voltage) ÷ I (current) = R (resistance)

Ohm’s Law Example Problems

Find the resistance of the circuit. By looking at this circuit we know the values of two components: voltage (12v) and resistance (3 ohms). How do we find current?

We plug our known values into our formula wheel and work the equation.

12 volts ÷ 3 ohms = 4 amps

For another example, find a circuit’s resistance from these values:

Voltage = 120v

Current = 17 amps

Use the known values in the formula wheel and solve the equation.

120 volts ÷ 17 amps = 7.05 ohms

That calculation is easier than installing a whole house surge protector.

It might take some practice, though it’s certainly simpler than fitting a refrigerator surge protector – which is just plug and play.

Principle’s of Ohm’s Law – Proportional and Inversely Proportional

Ohm’s Law follows this relationship:

that the electrical current (I) flowing in an circuit is proportional to the voltage (V) and inversely proportional to the resistance (R).

This means that if the voltage is increased then the current will increase as long as the resistance doesn’t change. If the resistance is increased and voltage remains the same, then the current will decrease.

Increasing Resistance

120 volts ÷ 5 ohms = 60 amps

120 volts ÷ 10 ohms = 12 amps

120 volts ÷ 20 ohms = 6 amps

Therefore, if the voltage is increased, the current will increase provided the resistance of the circuit does not change.

Increasing Voltage

120 volts ÷ 25 ohms = 4.8 amps

240 volts ÷ 25 ohms = 9.6 amps

480 volts ÷ 25 ohms = 19.2 amps

As you can see when we increase the voltage and leave the resistance the same, the current increased (directly proportional to the voltage).

Ohm’s Law PIE Formula Chart

The PIE chart works like the formula wheel for voltage, current and resistance. Power is measured in watts and is defined as:

the rate at which work is done when one ampere (A) of current flows through an electrical potential difference of one volt (V)

Formula Wheel with Ohm’s Law and PIE

This formula wheel combines Ohm’s Law with the PIE formula.

Although it looks more complicated, it works like the previous charts. It’s easy to use, though you may need a calculator.

The formula wheel is divided into four sections, each section has three formulas. If you need to find volts then you would use the E section, current – the I section, resistance – the R section, and power – the P section.

When using the formula wheel you need to follow these steps:

Know what you’re trying to solve for: current (I), voltage (E), resistance (R) or power (P).
Identify the known values (you need two): current (I), voltage (E), resistance (R) or power (P)
Find the section of the formula wheel that your values plug into.
Solve the equation

Use compatible values in your calculations. Convert kilohms to ohms and milliamperes to amperes.

Whether you’re an electrician apprenticeship or Journeyman electrician, you need to learn Ohm’s law to do an electrician’s work.