๐งฉ Resistor Series/Parallel Calculator
Enter the values of multiple resistors to calculate the total (equivalent) resistance when connected in series or in parallel. Add or remove resistors freely.
How to use
- Choose series or parallel.
- Enter each resistorโs value (ฮฉ). Use "Add resistor" to add more.
- The total resistance is calculated automatically.
How the calculation works
This tool works out the overall resistance (equivalent resistance) of several resistors connected together. Series: R = R1 + R2 + R3 + โฆ Parallel: 1/R = 1/R1 + 1/R2 + 1/R3 + โฆ In series, the same current flows through every resistor, so the values simply add up. In parallel, the current splits across more paths, so the combined resistance is lower than the smallest resistor. n identical resistors in parallel give 1/n of one resistor. A 0 ฮฉ resistor (a short) in a parallel group takes all the current, so the result is 0 ฮฉ. Empty or non-numeric rows are left out of the calculation.
Worked example
100 ฮฉ, 220 ฮฉ and 330 ฮฉ Series: 100 + 220 + 330 = 650 ฮฉ Parallel: 1 รท (1/100 + 1/220 + 1/330) โ 56.9 ฮฉ Two 100 ฮฉ resistors in parallel give 50 ฮฉ; four give 25 ฮฉ. To make a value you do not have, combine what you do: two 1 kฮฉ resistors give 2 kฮฉ in series and 500 ฮฉ in parallel.
Things to be aware of
- The accuracy of the result is limited by the tolerance of the resistors (ยฑ1%, ยฑ5% and so on). Combining them does not reduce the percentage error.
- Resistors in parallel share the heat (power). If power is tight, check each resistorโs power rating too.
- For circuits that mix series and parallel, work from the innermost group outward and treat each result as a single resistor.
FAQ
What formulas are used for series and parallel?
Series is the simple sum of resistances (R = R1 + R2 + ...). Parallel is the reciprocal of the sum of reciprocals (1/R = 1/R1 + 1/R2 + ...).
What happens to total resistance in a parallel circuit?
The total resistance of a parallel combination is always smaller than the smallest individual resistor value.
How many resistors can I add?
You can add as many resistors as you like using the "Add resistor" button โ thereโs no upper limit.