• Questionnaire
  • Save

Series and parallel resistor circuits are a part of a standard science study. Problems usually require you to calculate the total resistance of a circuit or ask for an equivalent resistance using the best combination of resistors.

Our Parallell Resistor Calculator helps you find the total equivalent resistance in a parallel circuit or series of resistors. Simply enter the resistances separated by commas to generate a result.

For those just learning, we have prepared the ultimate Q&A for our parallel resistance calculator. We cover resistor basics, calculating resistance and more.


What can a parallel resistor calculator do?

In electronic circuits, resistors have many uses. They are used to reduce current flow, adjust signal levels and to terminate transmission lines. There are many other uses too.

Any electrical device today might have hundreds of circuits. Calculating the power, amperage, resistance, and voltage by hand is both tedious and prone to error.

Our parallel resistor calculator eliminates mistakes in transcription and helps you verify your answers. It'll provide you with the equivalent resistance for resistors connected in parallel or series.

We hope this short explanation and our calculator are useful to you. Save this page to the home screen of your smartphone, for quick and easy access to this great tool.

What are parallel and series resistors?

Before diving in, it's important to first understand what an individual resistor is. It is a two-terminal electrical component.

It is the part of a circuit that implements electrical resistance. It consumes but does not produce energy.

Parallel and Series Circuit Diagram

Parallel resistors are created when a circuit shares two current paths (or more) to a common power source. For example, four resistors in parallel with a battery:

Current flows to R1, R2, R3, and R4 from the positive battery terminal. The node that is connecting R1 to the battery also connects R2, R3, and R4. The other ends of these resistors are connected likewise, then tied to the negative terminal of the battery.

There are four unique paths that current can take before it returns to the battery. The resistors are considered parallel. Parallel components all have equal voltage drop, current may not be the same between resistors.

Characteristics of resistors connected in parallel:

  • A parallel circuit has two or more paths for current to flow through
  • Voltage drop is equal across each component of the parallel circuit
  • Total current equals the sum of each current path
  • If one of the paths in a parallel circuit is broken, current continues to flow in the remaining paths

This is different from a series circuit.

Characteristics of a resistors in series circuit:

  • A series circuit has one path for current to flow
  • If the circuit is broken at any point, no current will flow
  • The total resistance of a series circuit is equal to the sum of individual resistances. R total = R1 + R2 + R3...
  • The voltage applied to a series circuit is equal to the sum of the individual voltage drops

What is the formula for resistors in a parallel?

The formula for total resistance in a parallel circuit is calculated in the following way:

1/Rt = 1/R1 + 1/R2 + 1/R3 +...

Rt = R total


Let's calculate the resistance of a parallel circuit with three paths (it could be any number larger than two). The power source is providing 9 volts and the value of the resistors are 4 Ohms, 4 Ohms, and 2 Ohms.

  • E = 9V
  • R1 = 4 Ohm
  • R2 = 4 Ohm
  • R3 = 2 Ohm


1/Rt = 1/R1 + 1/R2 + 1/R3 +...


1/Rt = 1/4 + 1/4 + 1/2

1/Rt= 1

Rt = 1 ohm

What other problems can parallel resistance solve?

Once you have the total resistance of a circuit, you can calculate the amperage using Ohm's Law.

Returning to the above example you can use Ohm's Law to figure out the total amperage (I):

I = Voltage / Resistance

I = 9V / 1 Ohm

= 9 Amps

The total amperage between the three resistor branches must equal 9 Amps. To figure out what each branch pulls, use Ohm's Law again.

Reminder: the voltage is the same everywhere in a parallel circuit. So we know the voltage and the resistance:

I1 = 9V / 2 Ohm = 4.5 A

I2 = 9V / 4 Ohm = 2.25 A

I3 = 9V / 4 Ohm= 2.25 A

To doublecheck your answer, take the I total above and plug in your figures.

It = I1 + I2 + I3...

9 Amps = 4.5 A + 2.25 A + 2.25A

Once you have Voltage, Ohms, or Amps, you can calculate Power (Watts) with any two of those variables.

P = I (current) * E (voltage)

P = E2 / R (resistance)

P = I2 * R

P (total) = P1 + P2 + P3 ...

Of course, use a second equation or an online calculator to check your answers.

Tell your friends about us!