Our series resistor calculator is the perfect tool to find the equivalent resistance of a circuit consisting of up to ten resistors connected in series.

This calculator can also be called equivalent resistance calculator for resistors in series or circuit resistance calculator.

Keep reading while we show you the series resistance formula and how to calculate resistance in a series circuit. Let's begin!

What is a resistor?

A resistor is an electrical component that resists the current flow within a circuit.

Ohm's law indicates how much a resistor impedes this flow of current:

V=I×RV = I\times R


  • VV is the voltage difference across the resistor, in volts;
  • RR is the resistor's resistance in ohms (the series resistor calculator has a built-in unit switcher, allowing you to input resistance in other units); and
  • II is the resulting current, in amperes.

💡 As current flows through a resistor, the resistor gets heated. Read more about this in the power dissipation calculator!

How to calculate resistance in a series circuit — resistors in series formula

When we connect resistors in series, the current is the same through each of them. Because of that, we can find the total voltage drop across the resistors by adding the individual voltages across each resistor:

V=V1+V2+...+VnV=IR1+IR2+...+IRn{\small V = V_{1} + V_{2} + ... + V_{n}} \\ {\small V = I R_{1} + I R_{2} + ... + I R_{n}}


  • VV is the total voltage difference across all the resistors.
  • ViV_{i} are the individual voltage differences.
  • II is the current flowing through the resistors.
  • RiR_{i} are the individual resistances. You can input up to ten resistors in our series resistor calculator.

🔎 Look at our parallel resistor calculator and see how it differs from this tool!

Notice that here the current is a common II factor in every term, and if we factor out this current, we're left with:

V=I(R1+R2+...+Rn)V = I (R_{1} + R_{2} + ... + R_{n})

This expression looks a lot like Ohm's law, and if we group all these resistances in a single term, the similarity becomes more evident:

V=IReqV = I R_{eq}

ReqR_{eq} is what we call the equivalent resistance of the circuit.

When we connect the resistors in series, the equivalent resistance acts as a single resistance equal to the sum of all the individual resistances as seen in the resistors in series formula:

Req=R1+R2+...+RnR_{eq} = R_{1} + R_{2} + ... + R_{n}

🙋 Use our series resistor calculator to find the equivalent resistance easily! Simply input the resistance of each resistor, and our equivalent resistance calculator will do the rest.

Other features of our series resistor calculator

This calculator already has the series resistance formula within it, and it's smart enough to find the missing resistance given the equivalent resistance and all other resistance values.

Select the calculate missing resistor mode and experiment with it!

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