Find the total resistance of resistors in series or in parallel — free, with a circuit diagram.
Resistors in series simply add up: Rₜₒₜₐₗ = R₁ + R₂ + R₃ + … — the same current flows through each one in turn, so their resistances stack.
Resistors in parallel combine differently, since the current splits across multiple paths: 1/Rₜₒₜₐₗ = 1/R₁ + 1/R₂ + 1/R₃ + … The total is always *less* than the smallest individual resistor — adding more parallel paths only gives current more ways to flow, never fewer.
Enter as many resistors as your circuit has, switch between series and parallel, and this computes the combined total along with a diagram of how they're connected.
Adding a parallel path gives current an additional route, which can only make it easier (never harder) for current to flow overall — so the combined resistance can only go down, never up, as you add more parallel resistors.
Two equal resistors in parallel always combine to exactly half of one resistor’s value — for example, two 100Ω resistors in parallel give 50Ω.
Not directly in this tool — it handles a single group of resistors either all in series or all in parallel. For a mixed circuit, simplify each series or parallel section separately, then combine those results.