Parallel Resistance Calculator – Two Resistors (Ω)
Find the equivalent resistance of two positive resistors in parallel with R = R1×R2/(R1+R2), with a worked 100Ω and 200Ω example.
Two resistors connected in parallel give current more than one branch to follow. Their equivalent resistance is lower than either individual positive resistor. The calculator accepts precisely two positive resistance values in ohms, not a multi-branch circuit.
How it works
For two positive resistors, 1/R = 1/R1 + 1/R2, or equivalently R = (R1 × R2) ÷ (R1 + R2).
Example
For a 100 Ω and 200 Ω pair, equivalent R = 100 × 200 ÷ 300 = approximately 66.67 Ω.
How to use
- Enter the first resistor's resistance in ohms.
- Enter the second resistor's resistance in ohms; both inputs must be greater than zero.
- Check that the equivalent resistance is smaller than the smaller entered resistor for a valid two-resistor parallel circuit.
Key features
- Two-resistor reciprocal relationship
- Positive-resistance validation
- Result in ohms
Common uses
- Verify school circuit calculations
- Plan two-resistor electronics experiments
- Compare equivalent resistance with a series combination
Limitations to know
This tool only models two ideal positive-valued resistors. It does not model tolerances, temperature effects or a larger network. A short circuit with zero resistance is outside the accepted input range.
Frequently asked questions
Why is the answer less than 100 Ω?
Parallel branches reduce equivalent resistance; 100 Ω in parallel with 200 Ω gives about 66.67 Ω.
Can I add resistor values instead?
Adding resistance values is the series-resistor calculation, not the parallel calculation.
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