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Series Resistance Calculator

Total resistance of resistors in series

How it is calculated

When resistors are connected end to end, the same current flows through each of them and their resistances simply add: Rtotal = R1 + R2 + R3 + R4, all in ohms (Ω). The tool has four slots; for fewer resistors enter 0 in the unused ones. Values cannot be negative and the total must be above zero. The result is exact arithmetic on the nominal values you type, so real resistor tolerances (for example ±5%) are not included. The total is always larger than the largest single resistor.

Worked example

Four resistors of 100 Ω, 220 Ω, 330 Ω and 47 Ω are in series. Add them: 100 + 220 = 320, plus 330 = 650, plus 47 = 697.00 Ω. At 12 V the current would be about 17 mA (12 ÷ 697).

Try this example →

Common mistakes

  • Leaving unused slots empty instead of 0. All four fields must contain a number.
  • Using this for resistors in parallel. Parallel branches combine through reciprocals and give a total smaller than the smallest resistor.
  • Mixing kΩ and Ω, for example 4.7 for 4.7 kΩ next to 220 for 220 Ω. Convert everything to one unit first.
  • Ignoring tolerance, so the measured total differs slightly from the nominal sum.

About this calculator

Resistors wired in series share the same current, so their resistances simply add: R_total = R1 + R2 + R3 + R4 — this tool adds up to four resistors chained end-to-end (enter 0 in any slot you do not use), and the total opposition to current climbs with each one you add.

Electronics hobbyists and students use it constantly when building circuits on a breadboard, since it's the fastest way to check a series combination against a target resistance — for LED current-limiting resistors, voltage dividers, or simply combining odd-value resistors from a parts bin to hit a value you don't have on hand.

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Comments (1)

  • Editorial team

    The total tells you the resistance, but check the power too. In a series chain every resistor carries the same current, so each one dissipates I squared times R. In the guide's 12 V example the current is about 17 mA, so the 330 ohm part gets roughly 0.098 W, comfortably inside a quarter-watt rating. Raise the voltage and that margin shrinks quickly. What target value are you trying to reach from your parts bin?

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