Combines up to four resistors wired in parallel into a single equivalent resistance value.
How it works
The reciprocal of the total resistance equals the sum of the reciprocals of each individual resistor.
What this does not include
This does not include resistors wired in series (which simply add directly) — this calculator specifically handles the parallel wiring case.
How to use this calculator
- Enter two to four resistor values in ohms.
A worked example
Two resistors, 100Ω and 200Ω, in parallel: 1/Rtotal = 1/100 + 1/200 → Rtotal = 66.6667Ω — lower than either resistor alone.
Three 10Ω resistors in parallel → Rtotal = 3.3333Ω.
What the variables mean
| Variable | Meaning |
|---|---|
| R1, R2, R3, R4 | Individual resistor values, in ohms (unused slots left blank) |
Edge cases worth knowing
Total resistance in parallel is always less than the smallest individual resistor. Adding more parallel paths only ever lowers the total, never raises it — the opposite of resistors in series.
A resistor value of zero shorts the circuit — the total resistance collapses to zero, which the calculator flags as an invalid rather than a real result.
Frequently asked questions
Why is the equivalent resistance always less than the smallest resistor?
Because adding a parallel path always gives current more routes to flow through, which always reduces the total resistance below any single branch.
What if only two resistors are equal?
Two equal resistors in parallel always combine to exactly half of one resistor’s value.
How is this different from resistors in series?
In series, resistances simply add together; in parallel, it’s the reciprocals that add, which is why the combined result is always smaller than any individual resistor.
