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Electrical Calculators

Parallel Resistor Calculator

Verified formula Updated Jun 2026 Private — runs on your device

Enter details
Ω
Ω
Verified formula Private

Combined resistance

66.667

For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.

How to use the Parallel Resistor Calculator

The Parallel Resistor Calculator works out your combined resistance in an instant. Enter resistor r1 and resistor r2 and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.

  1. Enter the resistor r1.
  2. Enter the resistor r2.
  3. Read off your combined resistance — the calculator updates automatically, with no button to press.

Formula

The Parallel Resistor Calculator uses the formula:

Combined resistance = Resistor R1 × Resistor R2 ÷ (Resistor R1 + Resistor R2)

Worked example

For example, with resistor r1 of 100 Ω and resistor r2 of 200 Ω, the combined resistance is 66.667.

Inputs used
Resistor R1 100 Ω
Resistor R2 200 Ω
Results
Combined resistance 66.667

Results are estimates for educational use, not professional advice.

Frequently asked questions

For two resistors, R = R1 × R2 ÷ (R1 + R2). A 100 Ω and 200 Ω resistor in parallel give about 66.67 Ω.

Parallel paths give current more routes to flow, so the combined resistance is always less than the smallest resistor.

Add the reciprocals: 1 ÷ R = 1 ÷ R1 + 1 ÷ R2 + … then invert. This tool handles the common two-resistor case.

Two equal resistors in parallel give exactly half the value. Two 100 Ω resistors make 50 Ω.

Enter the resistor r1. Enter the resistor r2. Read off your combined resistance — the calculator updates automatically, with no button to press.

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