Parallel Resistance Calculator
Calculate parallel resistance step by step: 1 ÷ R_total = 1 ÷ R1 + 1 ÷ R2 + … + 1 ÷ Rn.
In short
Calculate parallel resistance step by step: 1 ÷ R_total = 1 ÷ R1 + 1 ÷ R2 + … + 1 ÷ Rn.
Formula: 1 ÷ R_total = 1 ÷ R1 + 1 ÷ R2 + … + 1 ÷ Rn. For two: R1·R2 ÷ (R1 + R2).
Total resistance
68.75 Ω
- Total conductance
- 0.014545 S
- Resistors counted
- 2
What this calculator does
Calculate parallel resistance step by step: 1 ÷ R_total = 1 ÷ R1 + 1 ÷ R2 + … + 1 ÷ Rn. Worked example, questions and limitations included.
You enter r1, r2, r3 (optional) and r4 (optional) and a few other details, and the parallel resistance calculator shows the answer along with the working, so you can check it or try other numbers.
The page shows the formula, a numeric worked example, and the assumptions that affect this electrical calculation.
Inputs and what they mean
- R1
- — number value.
- R2
- — number value.
- R3 (optional)
- — number value.
- R4 (optional)
- — number value.
- R5 (optional)
- — number value.
How to use it
- Enter each value in the unit shown next to the box (use the unit converter first if your numbers are in other units).
- Check the breakdown to see every intermediate step.
- Read the limitations before relying on the result.
Formula
Every resistance must be above zero (a zero-ohm branch is a short circuit).
The total is always smaller than the smallest branch.
Blank optional boxes are skipped.
1 ÷ R_total = 1 ÷ R1 + 1 ÷ R2 + … + 1 ÷ Rn. For two: R1·R2 ÷ (R1 + R2).
Inputs used: R1, R2, R3 (optional), R4 (optional), R5 (optional).
Worked example
100 Ω ∥ 220 Ω
- 1/100 + 1/220 = 0.014545 S.
- R = 1 ÷ 0.014545 = 68.75 Ω.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- Up to five branches.
- Ignores tolerance and temperature drift.
- Ideal connections assumed.
- Results are estimates for planning and learning. Real designs, installations and bids must be checked by a qualified, licensed professional against the codes that apply where you work.
- The result depends on the values you enter for this parallel resistance calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Reference: OpenStax (Rice University)
Last reviewed:
Common questions
Why is the result smaller than every resistor?
Each extra branch gives current another path, so the combination conducts more easily than any one branch alone.
What happens with a 0 Ω branch?
It is a short circuit and the total becomes zero, so the calculator asks for values above zero.
How do I get an unusual value?
Combining standard resistors in parallel or series is a common way to reach values that are not sold individually.
How do I use the Parallel Resistance Calculator?
Enter the required values for R1, R2, R3 (optional), R4 (optional), R5 (optional). The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the Parallel Resistance Calculator use?
1 ÷ R_total = 1 ÷ R1 + 1 ÷ R2 + … + 1 ÷ Rn. For two: R1·R2 ÷ (R1 + R2). The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.
Can the Parallel Resistance Calculator be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
Sources
Method based on OpenStax (Rice University).
Cite this page
Free Calculator. (2026, November 3). Parallel Resistance Calculator. https://freecalculator.tech/tools/parallel-resistance-calculator
"Parallel Resistance Calculator." Free Calculator, 3 Nov. 2026, https://freecalculator.tech/tools/parallel-resistance-calculator.
Parallel Resistance Calculator — Free Calculator, https://freecalculator.tech/tools/parallel-resistance-calculator
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