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Parallel & Series Resistor Calculator

Calculate total resistance of resistors in parallel or series with unlimited values. Also works for capacitors, where the series/parallel rules invert.

R1
R2
68.75 Ω
Total (2 in parallel)
1/X = Σ(1/Xi)
Rule used

Result

Parallel resistors: reciprocals add, so the total is always below the smallest resistor. Product over sum: (100 Ω × 220 Ω) ÷ (100 Ω + 220 Ω) = 68.75 Ω.

What is the Parallel & Series Resistor Calculator?

The ByteTools Parallel & Series Resistor Calculator combines any number of resistors into a single equivalent value.

  • Any number of components with add/remove rows
  • Series and parallel modes for resistors and capacitors
  • Unit prefixes: mΩ to MΩ, pF to mF
  • Two-resistor product-over-sum shortcut displayed
  • Result always below the smallest resistor in parallel mode — a built-in sanity check
  • 100% private — runs entirely in your browser

How to use the Parallel & Series Resistor Calculator

  1. 1

    Choose resistors or capacitors, and series or parallel.

  2. 2

    Enter each component value and unit prefix, adding rows as needed.

  3. 3

    Read the combined equivalent value, updated live.

  4. 4

    With two resistors in parallel, check the product-over-sum shortcut shown.

  5. 5

    Copy the result with one click.

About the Parallel & Series Resistor Calculator

The ByteTools Parallel & Series Resistor Calculator combines any number of resistors into a single equivalent value. In series the resistances simply add (Rtotal = R1 + R2 + …); in parallel the reciprocals add (1/Rtotal = 1/R1 + 1/R2 + …). Add as many rows as your network needs, each with its own Ω/kΩ/MΩ prefix.

It also has a capacitor mode, where the rules invert: capacitors add in parallel and combine by reciprocals in series. For quick mental checks, the classic two-resistor shortcut Rtotal = (R1 × R2) ÷ (R1 + R2) is shown whenever you have exactly two values.

All calculations happen 100% locally in your browser. Nothing is uploaded, results update as you type, and the tool works offline.

Frequently asked questions

How do you calculate resistors in parallel?

Add the reciprocals and invert: 1/Rtotal = 1/R1 + 1/R2 + …. For 100 Ω in parallel with 220 Ω, 1/Rtotal = 1/100 + 1/220 = 0.014545, so Rtotal = 68.75 Ω. The parallel total is always smaller than the smallest individual resistor.

What is the product-over-sum formula?

For exactly two resistors, the parallel combination simplifies to Rtotal = (R1 × R2) ÷ (R1 + R2). Using 100 Ω and 220 Ω: (100 × 220) ÷ 320 = 68.75 Ω — the same answer as the reciprocal method, just faster for two values.

Why do capacitors follow the opposite rules to resistors?

Capacitance is charge stored per volt. Capacitors in parallel share the same voltage and their plate areas effectively add, so C = C1 + C2. In series the same charge spans multiple gaps, so the reciprocals add instead — exactly the mirror image of resistors.

What happens if all parallel resistors are equal?

N equal resistors of value R in parallel give R ÷ N. Two 1 kΩ resistors make 500 Ω; four make 250 Ω. This is a handy way to build non-standard values or share power dissipation across several parts.

Does the order of resistors matter?

No. Both series addition and parallel reciprocal addition are commutative, so components can be listed in any order without changing the equivalent value. Physical layout matters for other reasons (heat, parasitics) but not for the DC resistance.

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