Parallel Resistor Calculator
Enter two resistor values and get their combined resistance in parallel — the single number behind current sharing, voltage dividers, and load design.
Two values, one answer
Enter both resistor values in ohms and the calculator returns the parallel total with the product-over-sum rule, Rp = (R1 × R2) ÷ (R1 + R2).
Always smaller
The parallel total is always smaller than the smaller of your two resistors — adding a second path makes it easier for current to flow.
What does parallel resistance mean?
Two resistors, one combined value
Two resistors are wired in parallel when they share the same two connection points, so the current arriving at the junction can split and flow through either one. Together they behave like a single resistor whose value you get from the product-over-sum rule, written Rp = (R1 × R2) ÷ (R1 + R2). Because the current now has two routes instead of one, the pair always offers less resistance than either resistor on its own. That is the opposite of a series connection, where the resistors sit end to end and you simply add them. Parallel combinations show up constantly in real circuits — sharing current between components, trimming a load's resistance, and building a value you do not have from two you do.
Enter both resistances in ohms to get the combined parallel resistance instantly.
One short formula, built from the two resistor values R1 and R2.
Rp = (R1 × R2) ÷ (R1 + R2)Multiply the two resistances to get the product, add them to get the sum, then divide the product by the sum. The "product over sum" shortcut is the two-resistor case of the more general parallel rule (1 ÷ Rp = 1 ÷ R1 + 1 ÷ R2); for exactly two resistors it is the quickest form to work by hand.
Suppose you wire a 4 Ω resistor in parallel with another 4 Ω resistor.
Product
4 × 4 = 16 — multiply the two resistances together.
Sum
4 + 4 = 8 — add the two resistances together.
Divide
16 ÷ 8 = 2 Ω — the combined parallel resistance, half of one resistor.
The combined value tells you how the pair behaves as a single resistor, and the first thing to notice is that it is always smaller than the smaller of your two resistors. That is not a quirk of the formula — it is the physics. Adding a second path for the current to take makes the whole combination easier to push current through, so the resistance drops. Two equal resistors are the easy case: the parallel total is exactly half of one of them, which is why 4 Ω and 4 Ω give 2 Ω, and 100 Ω with 100 Ω give 50 Ω. When the two values differ, the result leans toward the smaller one — a 2 Ω resistor in parallel with an 8 Ω resistor gives 1.6 Ω, much closer to 2 than to 8, because most of the current takes the easier 2 Ω path. This is the exact opposite of a series connection, where resistances add and the total grows. Whenever you need to lower a resistance or share current between two components, reaching for a parallel pair is the move.
The product-over-sum rule is exact for two ideal resistors, but a couple of practical points are worth keeping in mind.
Two resistors, ideal and ohmic
This calculator combines exactly two resistors. For three or more in parallel, apply the rule in stages (combine the first two, then put the result in parallel with the third) or use the general reciprocal form. Keep both values in the same unit — ohms here — and remember the formula assumes ideal, ohmic resistors; real components carry a tolerance, and wires and connections add a small resistance of their own. Diodes, LEDs, and other non-ohmic parts do not follow this rule.