Series & Parallel Resistor Calculator
Find the total resistance of resistors in series or in parallel.
About the Series & Parallel Resistor Calculator
Type the resistor values separated by spaces; you can use k and M, such as 4.7k or 1M. The calculator gives the total resistance with the resistors wired in series and wired in parallel.
In series, resistances add. In parallel, their reciprocals add, so the total is always less than the smallest resistor. Two equal resistors in parallel give half the value.
The formula
Series: R = R₁ + R₂ + …; parallel: 1/R = 1/R₁ + 1/R₂ + …
Worked example
100 Ω, 220 Ω and 470 Ω
- Series: 100 + 220 + 470 = 790 Ω
- Parallel: 1 ÷ (1/100 + 1/220 + 1/470) = 59.98 Ω
- Two 1 kΩ resistors in parallel: 500 Ω
Things to keep in mind
- For a mixed network, work out each series or parallel group first, then combine the results.
Questions people ask
Two resistors in parallel?
R = R₁ R₂ ÷ (R₁ + R₂).
Capacitors?
The rules swap: capacitors add in parallel.
Why combine resistors at all?
To make a value you don't have, or to share power across several parts.