Parallel Resistance Calculator
Equivalent resistance = R₁R₂ ÷ (R₁ + R₂)
Find equivalent resistance for two ideal resistors in parallel.
Formula
Equivalent resistance = R₁R₂ ÷ (R₁ + R₂)
Worked example
First resistance: 100 Ω
Second resistance: 200 Ω
With these inputs, the result is 66.6666667 Ω.
How to use this calculator
- Identify the quantity you want to calculate.
- Enter your measurements in the units shown on each field.
- Read the result, which updates as you change the inputs.
- Check the assumptions below before applying the result.
Assumptions and limits
Use consistent units and keep unrounded values until the final step.
Precision and checking
Results are rounded for display. Use the most accurate measurements available, and avoid rounding your inputs unnecessarily. Extra decimal places in a result do not make an estimate more reliable.
To check a result, substitute the same input values into the formula shown above. Change one value at a time to understand how the quantity responds.
Frequently asked questions
What assumptions does this calculation use?
Use consistent units and keep unrounded values until the final step.
Are my inputs sent to a server?
No. The calculation runs locally in your browser. The result updates as you edit the inputs.
Sources & references
- NIST Guide to the SI — National Institute of Standards and Technology
