Parallel resistor calculator
Parallel resistance is a reciprocal sum, so adding another path can only lower the total. Two 1 kΩ resistors give 500 Ω; adding a third gives 333 Ω. That is a useful sanity check — if your answer is larger than the smallest resistor in the set, the arithmetic has gone wrong somewhere.
Parallel resistance is the reciprocal of the sum of reciprocals: 1/R = 1/R₁ + 1/R₂ + … A 1 kΩ, 2.2 kΩ and 4.7 kΩ in parallel give 599.8 Ω. The result is always smaller than the smallest resistor in the set.
How to calculate parallel resistance
For two resistors the shortcut R₁R₂/(R₁+R₂) is quicker by hand, and for equal resistors the answer is simply the value divided by the count. Beyond that the reciprocal sum is unavoidable, which is why this is one of the most-used calculators in electronics. Note that the dissipation splits unevenly: the smallest resistor carries the most current and burns the most power, so it is the one whose wattage rating you must check.
Questions
1/R_total = 1/R₁ + 1/R₂ + … For two resistors, R = R₁R₂ ÷ (R₁ + R₂).