Physics
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Parallel Resistor Calculator.
Calculate equivalent resistance for two resistors in parallel.
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Equivalent resistance: 66.666667 Ω
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