About this calculator
Type your resistor values, choose series or parallel, and get the total resistance.
You can use k for thousands and M for millions, so 4.7k means 4,700 Ω.
Worked examples
Real numbers, worked out by the same calculator. Press “Use these numbers” to try one above.
Three in series: 100, 220 and 470 Ω
- Total resistance (series)
- 790 Ω
- In ohms
- 790 Ω
- Conductance
- 0.001266 S
3 resistors (100 Ω, 220 Ω, 470 Ω) in series have a combined resistance of 790 Ω.
Show the working
- In series, just add them: 100 + 220 + 470 = 790 Ω.
- The total is always larger than the largest resistor (470 Ω).
Two 100 Ω resistors in parallel
- Total resistance (parallel)
- 50 Ω
- In ohms
- 50 Ω
- Conductance
- 0.02 S
2 resistors (100 Ω, 100 Ω) in parallel have a combined resistance of 50 Ω.
Show the working
- In parallel, add the reciprocals: 1 ÷ R = 1/100 + 1/100 = 0.02.
- So R = 1 ÷ 0.02 = 50 Ω.
- The total is always smaller than the smallest resistor (100 Ω).
1k, 2.2k and 4.7k in parallel
- Total resistance (parallel)
- 599.767981 Ω
- In ohms
- 599.767981 Ω
- Conductance
- 0.001667 S
3 resistors (1 kΩ, 2.2 kΩ, 4.7 kΩ) in parallel have a combined resistance of 599.767981 Ω.
Show the working
- In parallel, add the reciprocals: 1 ÷ R = 1/1,000 + 1/2,200 + 1/4,700 = 0.001667.
- So R = 1 ÷ 0.001667 = 599.767981 Ω.
- The total is always smaller than the smallest resistor (1 kΩ).
Series
In a series circuit the same current flows through each resistor and the resistances simply add: R = R₁ + R₂ + R₃ + …. The total is always larger than the largest resistor.
Parallel
In a parallel circuit current splits between the branches and the reciprocals add: 1 ÷ R = 1 ÷ R₁ + 1 ÷ R₂ + …. The total is always smaller than the smallest resistor. Two equal resistors in parallel give half the value of one.
Using the result
Once you have the total resistance, Ohm's law (V = I × R) gives the current for a given voltage. Use the Ohm's law calculator for that step.
Frequently asked questions
What is the formula for two resistors in parallel?
R = (R₁ × R₂) ÷ (R₁ + R₂), which is the same as adding the reciprocals.
Why is parallel resistance smaller?
Each extra branch gives the current another path, so the overall resistance falls.
Can I type 4.7k?
Yes. k means thousands and M means millions.
How many resistors can I enter?
Up to 50.
Formulas tested against hand-worked answers. Last reviewed 29 September 2026. These calculators do arithmetic only; they are not financial, tax or legal advice.