Enter the resistances of the individual resistors into the calculator to determine the equivalent resistance.

Equivalent Resistor Formula

The following formula is used to calculate the equivalent resistance of resistors in series and parallel.

For resistors in series: Req = R1 + R2 + R3 + ... + Rn

For resistors in parallel: 1/Req = 1/R1 + 1/R2 + 1/R3 + ... + 1/RnVariables:

  • Req is the equivalent resistance (Ohms)
  • R1, R2, R3, ..., Rn are the resistances of the individual resistors (Ohms)

To calculate the equivalent resistance of resistors in series, simply add up the resistances of all the resistors. To calculate the equivalent resistance of resistors in parallel, take the reciprocal of each resistor's resistance, add these values together, and then take the reciprocal of the result.

What is an Equivalent Resistor?

An equivalent resistor refers to a single resistor that can replace multiple resistors in an electrical circuit, without changing the net resistance, current, or voltage levels in the circuit. It simplifies complex circuits into simpler forms for easier analysis. The value of an equivalent resistor can be calculated differently based on whether the original resistors are arranged in series or in parallel.

How to Calculate Equivalent Resistor?

The following steps outline how to calculate the Equivalent Resistor.

  1. First, determine the resistances of the individual resistors (R1, R2, R3, ..., Rn) in Ohms.
  2. Next, determine whether the resistors are connected in series or parallel.
  3. If the resistors are connected in series, use the formula Req = R1 + R2 + R3 + ... + Rn to calculate the equivalent resistance (Req) in Ohms.
  4. If the resistors are connected in parallel, use the formula 1/Req = 1/R1 + 1/R2 + 1/R3 + ... + 1/Rn to calculate the equivalent resistance (Req) in Ohms.
  5. Finally, calculate the Equivalent Resistor.
  6. After inserting the values of the resistances and calculating the result, check your answer with a multimeter or an online calculator.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

R1 = 10 Ohms

R2 = 20 Ohms

R3 = 30 Ohms

R4 = 40 Ohms

R5 = 50 Ohms