Parallel Resistance Calculator (Multiple)

How it is calculated

The tool adds the reciprocals of the resistances: G = 1/R₁ + 1/R₂ + 1/R₃ + 1/R₄ and then Rt = 1/G. All resistances are in ohms (Ω). G is the total conductance, shown in millisiemens (mS) as G × 1000. It also reports how many resistors it used.

R1 is required and must be greater than zero. R2, R3 and R4 are optional: a field that is empty, zero or negative is ignored and not counted, so there is no division by zero but also no warning that a value was dropped. The total is always lower than the smallest resistor used.

Common mistakes

• Adding the resistances as if they were in series. In parallel you add reciprocals; 100 + 220 + 470 = 790 Ω would be far too high.
• Entering a value in kΩ without converting. The fields are in ohms, so 4.7 kΩ must be typed as 4700.
• Typing 0 for a shorted or missing resistor and expecting it to count. A zero in R2 to R4 is skipped, so the answer is for the remaining resistors only.
• Expecting a total larger than the smallest resistor. If the answer is not lower than it, a value was entered wrongly.
• Forgetting that more than four resistors need to be combined in steps: calculate a group, then use that result as one input.