Parallel Resistance Calculator
Enter two resistances to compute their equivalent parallel resistance R = (R1·R2)/(R1 + R2).
Input Data
Results
At a glance:Resistors in parallel share the same voltage; the total current is the sum, giving 1/R_eq = 1/R1 + 1/R2 + ... For two resistors, R_eq = (R1·R2)/(R1 + R2). The equivalent is always smaller than the smallest individual resistor (more paths → less total resistance). As one resistor → ∞ (open), R_eq → the other; if equal R1=R2=R, R_eq = R/2. This rule extends to N resistors via the reciprocal sum. This tool computes the two-resistor equivalent.
Formula
1/R_eq = 1/R1 + 1/R2
R_eq = (R1·R2)/(R1 + R2)
$$R = \frac{R_1 \cdot R_2}{R_1 + R_2}$$How to Use
- Enter resistance R1 (Ω).
- Enter resistance R2 (Ω).
- The calculator returns the equivalent R.
Case Studies
Two equal resistors
R1 = R2 = 100 Ω.
R_eq = 100×100/200 = 50 Ω.
Half of each, as expected.
FAQ
Why is parallel resistance smaller?
Adding a parallel path gives current more ways to flow, reducing total resistance below any single branch.
What if one resistor is very large?
It contributes little; R_eq approaches the smaller resistor. If R1→∞, R_eq→R2.
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References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.