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Parallel Resistor Calculator.

Calculate equivalent resistance for two resistors in parallel.

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Equivalent resistance: 66.666667 Ω

Equivalent resistance

0.000000Ω

Results update automatically as you type.

Use Cases

Designing parallel resistor networks

Quickly find the total resistance when combining two resistors in parallel, useful for circuit design and prototyping.

Example: If you have a 100 Ω and a 200 Ω resistor, the equivalent resistance is 66.67 Ω.

Checking circuit calculations

Verify your manual calculations for parallel resistance to ensure accuracy in homework or project work.

Example: Enter 330 Ω and 470 Ω to confirm the total is about 193.9 Ω.

Frequently Asked Questions

How do I calculate the equivalent resistance of two resistors in parallel?
Use the formula: 1/R_total = 1/R1 + 1/R2. For two resistors, you can also use the product-over-sum formula: R_total = (R1 * R2) / (R1 + R2). Enter the resistance values in ohms and the calculator will compute the result.
Why is the equivalent resistance less than the smallest resistor?
In a parallel circuit, current has multiple paths to flow, so the overall resistance decreases. The equivalent resistance is always less than the smallest individual resistance because adding a parallel path reduces the total opposition to current.
Can I use this calculator for resistors with different units?
This calculator expects both resistance values in ohms (Ω). If your resistors are in kilo-ohms or mega-ohms, convert them to ohms first (e.g., 1 kΩ = 1000 Ω) to get accurate results.

Tips & Common Mistakes

Tips

  • Ensure both resistance values are in ohms (Ω) before entering them. Convert kΩ or MΩ to Ω if needed.
  • If you have more than two resistors, calculate the equivalent of two at a time, then combine the result with the next resistor.
  • For equal resistors in parallel, the equivalent resistance is simply the value divided by the number of resistors (e.g., two 100 Ω in parallel give 50 Ω).
  • Use the product-over-sum formula (R1*R2)/(R1+R2) for a quick manual check when only two resistors are involved.

Common Mistakes to Avoid

  • Forgetting to convert units: entering values in kΩ or MΩ without converting to Ω will give incorrect results.
  • Using the series formula (R1 + R2) instead of the parallel formula, which would overestimate the resistance.
  • Entering zero or negative resistance values, which are not physically meaningful for standard resistors.

Last updated: August 13, 2026