Parallel Resistor Calculator
Calculate equivalent resistance for two parallel resistors.
Formula
For two resistors, Req = R1R2/(R1+R2).
How Parallel Resistance Works
Parallel resistors share the same voltage while current divides among branches. Adding a parallel path increases total conductance, so equivalent resistance is always lower than the smallest individual resistor.
Example Calculation
For 100 Ω and 220 Ω in parallel, Req = 100 × 220 / (100 + 220) = 68.75 Ω.
Factors and Interpretation
Two equal resistors in parallel produce half the resistance of either one. A very large resistor placed in parallel with a much smaller resistor changes the equivalent value only slightly.
Frequently Asked Questions
Can equivalent resistance be larger than R1 or R2?
No. For positive resistors in parallel, the result is lower than the smallest branch resistance.
What if both resistors are equal?
The equivalent resistance is half of either resistor.
How do I handle more than two resistors?
Use 1/Req = 1/R1 + 1/R2 + 1/R3 + … for additional branches.
Related Tools
Formula and Practical Limits
For parallel resistors, reciprocal resistances add. The equivalent resistance is always lower than the smallest positive branch resistance. Real components have tolerances and power limits that can affect circuit behavior.