Parallel Resistance Calculator
Resistors in parallel share the same voltage and split the current, so their combined resistance is always smaller than the smallest single resistor. Enter any number of resistor values in ohms, separated by commas or spaces. The calculator adds the reciprocals and inverts the sum to give the total parallel resistance, along with the equivalent conductance.
Parallel resistance formula
1 / Rtotal = 1/R1 + 1/R2 + ... + 1/Rn
Rtotal = 1 / (sum of reciprocals)
Two-resistor case: Rtotal = (R1 * R2) / (R1 + R2)
Conductance is the reciprocal of resistance, measured in siemens. Conductances add directly in parallel, which is why the reciprocals sum.
Worked example
Three resistors of 100, 220, and 470 ohms in parallel: 1/Rtotal = 1/100 + 1/220 + 1/470 = 0.01 + 0.004545 + 0.002128 = 0.016673 S. Rtotal = 1 / 0.016673 = 59.98 ohms, lower than the smallest (100 ohms), as expected.
Parallel resistance: frequently asked questions
How do you calculate resistors in parallel?
The reciprocal of the total resistance equals the sum of the reciprocals of each resistor: 1/Rtotal = 1/R1 + 1/R2 + ... + 1/Rn. The total is always less than the smallest individual resistor.
Why is parallel resistance lower than any single resistor?
Each parallel branch gives current an additional path, so more current flows for the same voltage, which means less overall opposition. Adding any resistor in parallel can only reduce the total resistance.
What is the shortcut for two resistors?
For exactly two resistors the total is the product over the sum: Rtotal = (R1 R2) / (R1 + R2). This calculator handles any count, but the two-resistor formula is a handy special case.
How do I enter the resistor values?
Type the resistance of each resistor in ohms, separated by commas or spaces, in the input box. The calculator reads every value you list and combines them all.
Sources
- NIST: SI units (ohm, siemens).
- The parallel reciprocal-sum rule is a standard result of circuit theory.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.