Parallel Resistance Calculator Formula

Understand the math behind the parallel resistance calculator. Each variable explained with a worked example.

Use the Parallel Resistance Calculator

Formulas Used

Total Resistance

total_resistance = 1 / (1/r1 + 1/r2)

Variables

VariableDescriptionDefault
r1Resistor 1(Ω)100
r2Resistor 2(Ω)200

How It Works

Parallel Resistance

Resistors in parallel share the same voltage, and the reciprocals of their resistances add.

Formula

1/R_total = 1/R1 + 1/R2 + ...

For two resistors: R_total = (R1 * R2) / (R1 + R2)

The total is always less than the smallest individual resistor.

Worked Example

Two resistors in parallel: 100 Ω and 200 Ω.

r1 = 100r2 = 200
  1. 011/R = 1/100 + 1/200 = 0.01 + 0.005 = 0.015
  2. 02R = 1 / 0.015 = 66.67 Ω
  3. 03Or: R = (100 * 200) / (100 + 200) = 20000 / 300 = 66.67 Ω

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