Parallel & Series Resistor Calculator
Compute the series and parallel equivalent of several resistors at once — just enter the values separated by commas.
Disclaimer: This calculator is provided for general informational and educational purposes only, on an “as is” basis and without any warranty of accuracy or fitness for a particular purpose. Results may contain errors — always verify independently before relying on them in real designs. PartAndStock accepts no liability for any loss or damage arising from use of this tool, including when embedded on third-party sites.
How to use
- 1Enter the resistor values in Ω, separated by commas or spaces.
- 2The series (sum) and parallel equivalents are computed at the same time.
- 3For exactly two resistors in parallel, the product-over-sum rule Rₜ = R1·R2/(R1+R2) also applies.
How it works
Enter any number of resistor values and get both the series (sum) and the parallel equivalent resistance instantly.
How series and parallel combine
In series, resistors sit end to end and their values add directly — the equivalent is always larger than the biggest resistor. In parallel, current has multiple paths; conductances (1/R) add, so the equivalent is always smaller than the smallest resistor. Two equal resistors in parallel halve to R/2.
Where it's used
Series connections divide voltage or raise total resistance; parallel connections increase current-carrying capacity, spread power, or reach a non-standard value from two standard resistors. Parallel also raises total power rating because heat spreads across several parts.
Worked examples
- Series: 1 kΩ + 2.2 kΩ + 4.7 kΩ = 7.9 kΩ
- Parallel: 1 kΩ ∥ 1 kΩ = 500 Ω (two equal → half)
- Parallel: 10 kΩ ∥ 10 kΩ ∥ 10 kΩ = 3.33 kΩ
Quick Rules
| Connection | Formula | Result direction |
|---|---|---|
| Series | Rₜ = ΣRᵢ | Above the largest |
| Parallel (2) | R1·R2/(R1+R2) | Below the smallest |
| Parallel (n equal) | R / n | One nth of R |