Series & Parallel Resistor Calculator Widget

Add a series and parallel resistor calculator to your website. Visitors enter up to eight resistors or capacitors, with shorthand like 4k7 or 100n, and see the equivalent value and how the current or voltage divides between them.

Electrical & Electronics Calculator Runs in your browser Free · no ads

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How it works

Resistors in series add; in parallel their conductances (1/R) add. Capacitors behave the other way round: in parallel they add, in series their reciprocals add. The widget applies the right rule for the component type and also shows each part's share - of the current for parallel resistors, of the voltage for series parts - so readers see which part dominates. Values accept metric prefixes, and for capacitors a plain number is read in the unit chosen (pF, nF, uF). Up to eight values can be combined, blanks are skipped, and the smallest and largest parts are listed for a quick sanity check.

Calculation method

  • Resistors in series: R = R1 + R2 + ... ; in parallel: 1/R = 1/R1 + 1/R2 + ...
  • Capacitors in parallel: C = C1 + C2 + ... ; in series: 1/C = 1/C1 + 1/C2 + ...
  • Share (parallel R): (1/Rn) / sum(1/R); share (series R): Rn / sum(R); series C voltage share: (1/Cn) / sum(1/C)
  • Ideal components: tolerance, ESR and leakage are not modelled; result to 5 significant figures with a metric prefix

Worked examples

Three resistors in parallel

Inputs: 100, 220 and 470 ohm in parallel

Result: 59.977 ohm; current shares 60%, 27.3% and 12.8%

1 / (0.01 + 0.004545 + 0.002128) = 59.98 ohm.

Two capacitors in series

Inputs: 10 uF + 10 uF in series

Result: 5 uF, each part carrying 50% of the voltage

1 / (1/10 + 1/10) = 5 uF.

Limitations

  • Pure series or pure parallel only - mixed networks such as a series pair in parallel with a third part must be reduced step by step.
  • Real capacitors in series also need balancing resistors for leakage; the voltage share shown assumes ideal parts.

Where publishers use it

  • Electronics courses and homework help on combining resistors
  • Hobbyists making an odd value from the resistors in the drawer
  • Audio and speaker-wiring guides
  • Capacitor bank and filter design notes

Questions

Why is the parallel result smaller than every resistor?

Each extra parallel path gives the current another way through, so the total resistance falls below the smallest single resistor.

Do capacitors follow the same rules?

The opposite ones. Capacitors in parallel add up, and in series the total is smaller than the smallest capacitor.

How do I enter 4.7 kilohms or 100 nanofarads?

Type 4.7k or 4k7, and 100n. Lower-case m is milli and upper-case M is mega.

What happens to the working voltage of capacitors in series?

It is shared in inverse proportion to capacitance, so a small capacitor in a series string sees the most voltage - the share column shows this.

What load do two 8-ohm speakers present?

Wired in parallel they present 4 ohm to the amplifier; in series, 16 ohm. The same rules apply to nominal speaker impedance, though a real driver's impedance varies with frequency, so check the amplifier's minimum rated load.

Cite or recommend this tool

If you reference this tool in an article, course or documentation, these formats are ready to copy. They are optional - nothing is added to your site unless you paste it.

A2Z Tools Series & Parallel Resistor Calculator
https://a2z.tools/embed/series-parallel-resistor

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