Parallel Resistor Calculator
Equivalent resistance for resistors in parallel (and in series, for comparison).
Quick answer
- Formula: 1/Rp = 1/R₁ + 1/R₂ + … ; Rs = R₁ + R₂ + … ; G = 1/Rp
- Worked example — Equivalent parallel resistance: 5.0000 Ω (full example below).
Parallel Resistor Calculator
| Equivalent parallel resistance | 5.0000 Ω |
| Equivalent series resistance | 20.0000 Ω |
| Total conductance | 0.200000 S |
| Number of resistors | 2 |
Two equal 10 Ω resistors in parallel give exactly half: 5 Ω, while in series they would give 20 Ω.
Resistors in parallel share the same voltage, so their currents add. The equivalent resistance is always smaller than the smallest individual resistor, which is why parallel paths lower total resistance.
Enter resistances in ohms separated by commas. The calculator also shows the series equivalent and the total conductance (the reciprocal of the parallel resistance, in siemens).
The formula
Worked example
Two equal 10 Ω resistors in parallel give exactly half: 5 Ω, while in series they would give 20 Ω.
The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.
Frequently asked questions
Why is parallel resistance always lower?
Each added resistor opens another path for current. More paths at the same voltage means more total current, and lower effective resistance (R = V ÷ I).
How do I calculate two resistors quickly?
For exactly two resistors use R = (R₁ × R₂) ÷ (R₁ + R₂) — the 'product over sum' shortcut, which is the two-resistor case of the general formula.
Category: Science calculators
Sources & methodology
This calculator applies the formula shown on this page exactly as written, using the standard definitions for its inputs. Results are computed from the values you enter — no data is stored — and are rounded only for display.
Content last reviewed by CalcHub Editorial.
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