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Parallel Resistance Calculator

Work out parallel resistance instantly with clear inputs, formula shown and shareable results.

About Parallel Resistance Calculator

In parallel the conductances add: 1/Rtotal = 1/R1 + 1/R2 + 1/R3. The equivalent resistance is therefore always smaller than the smallest branch, and each branch carries current inversely proportional to its resistance while sharing the same voltage.

Formula

Parallel resistance

1/Rtotal = 1/R1 + 1/R2 + 1/R3

Worked example

With the default values below, Parallel Resistance Calculator returns Equivalent resistance of 599.77. Change any input above and every figure here is recalculated in your browser.

Inputs used

Resistor 1
1,000 Ω
Resistor 2
2,200 Ω
Resistor 3
4,700 Ω
Applied voltage
12 V

Results

Equivalent resistance
599.77 Ω
Total current
0.02001 A
Total conductance
0.001667 S
Total power dissipated
0.24 W

Step by step

  1. 1Values used
  2. 2Parallel resistance
  3. 3Equivalent resistance= 599.77 Ω
  4. 4Total current= 0.02001 A
  5. 5Total conductance= 0.001667 S
  6. 6Total power dissipated= 0.24 W

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 6 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

Why is the result always below the smallest resistor?

Adding another path can only increase total current for a given voltage, and more current at the same voltage means less resistance.

What is the two-resistor shortcut?

R = R1 x R2 / (R1 + R2), the product over sum rule, which only works for exactly two resistors.

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