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Series Resistor Calculator

Created by Bogna Szyk and Álvaro Díez
Reviewed by Steven Wooding
Last updated: Jan 18, 2024


This series resistor calculator is a tool for determining the equivalent resistance of a circuit with up to ten resistors connected in series. If you need your resistors in parallel, you can read our parallel resistor calculator for that.

Resistors in series formula

A series circuit is characterized by a common current that flows through all of the resistors – there is only one path the current can follow. The equivalent resistance for this kind of circuit is a sum of all individual resistances:

R=R1+R2+...+Rn,R = R_1 + R_2 + ... + R_n,

where:

  • RR – Equivalent series resistance; and
  • R1R_1, R2R_2, ... RnR_n – Resistances of individual resistors numbered 11 to nn.

The units of all values are Ohms (symbol: Ω). 1 Ohm is defined as electrical resistance between two points that, when applied with a potential difference of 1 volt, produces a current of 1 ampere. Hence, 1 Ω=1 V/1 A\small 1\ \Omega = 1\ \text{V} / 1\ \text{A} or, in SI base units, (Ω=kgm2/(s3A2\small \Omega = \text{kg}\cdot \text{m}^2/(\text{s}^3 \cdot \text{A}^2).

The formula for calculating equivalent resistance in a series circuit is similar to that for equivalent total inductance in a series circuit.

How to calculate series resistance

  1. Establish the values of resistance for all resistors connected in series. For example, you can use three resistors of 4 Ω\small 4\ \Omega, 3 Ω\small 3\ \Omega, and 6 Ω\small 6\ \Omega, respectively.
  2. Input these values in our series resistor calculator.
  3. Read the result. In this example, R=4+3+6\small R = 4 + 3 + 6, hence R=13 Ω\small R = 13\ \Omega. Notice that the equivalent resistance is higher than any of the individual values for resistors in series.

Other uses of the series resistor calculator

The principle is the same as when determining capacitance in parallel or induction in series – you can use it for these calculations too. Just remember that the units are not the same!

If you would like to find out the value of power dissipated in the resistor, try the power dissipation calculator or resistor wattage calculator. You can also check out our wheatstone bridge calculator to learn how to measure unknown resistance.

FAQ

How do I calculate the equivalent series resistance?

To calculate the equivalent series resistance, follow a few simple steps:

  1. Calculate or choose the desired resistance values.
  2. Sum the resistances of the chosen components.

That's it: the equivalent series resistance is nothing but the sum of the single resistances!

What is the equivalent of resistors with R 1.5 kΩ, 300 Ω, and 0.7 kΩ?

The equivalent series resistance is 2,500 Ω or 2.5 kΩ. To calculate this result:

  1. Convert all values of resistance in ohm:
    • 1.5 kΩ = 1,500 Ω;
    • 0.7 kΩ = 700 Ω.
  2. Sum the values:
    R = 1,500 + 700 + 300 = 2,500 Ω

Why do we sum the resistances of resistors in series?

Resistors are simple current-to-voltage transducers; placing one or more of these devices after each other creates a series of voltage drops for a constant current flux. Since each voltage drop is independent of the other and measured at the ends of the devices, we can sum the voltage drops, modeling a series of resistors and voltage drops as a single device with a single drop.

Is resistance higher in series on in parallel?

The resistance is always higher in series. In fact, the equivalent resistance of a parallel is consistently lower than each of its components, while the equivalent resistance of a series of resistors is always higher than each of its components. If you need a higher voltage drop, always choose to put your resistors in series!

Bogna Szyk and Álvaro Díez
drawing of resistors in series in an electrical circuit
Mode
Calculate equivalent resistance
Resistor 1 (R₁)
Ω
Resistor 2 (R₂)
Ω
You can add up to 10 resistors, fields will appear as you need them.
Results
Input at least one resistor to obtain a result.
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