Reference · updated 10 November 2026
Parallel resistor calculator: total resistance
Enter two to six resistor values and the calculator gives the total resistance when they are wired in parallel, and also when they are wired in series. A parallel total is always smaller than the smallest resistor; a series total is the plain sum.
iPhone and iPad (iOS 17 or later): free on the App Store. Android later.
Parallel resistor calculator
This calculator needs JavaScript. Without it, use the formulas and the worked examples below.
Pick the unit of each resistor in its own box (Ω, kΩ or MΩ), so values such as 470 Ω and 4.7 kΩ can be mixed. A decimal point or a decimal comma both work. Leave unused rows empty; two values are the minimum.
The formulas
In series the resistances add up:
R = R1 + R2 + R3 + …
In parallel the conductances (1/R) add up:
1 ÷ R = 1 ÷ R1 + 1 ÷ R2 + 1 ÷ R3 + …
For exactly two resistors this reduces to R = (R1 × R2) ÷ (R1 + R2). For n equal resistors it is R ÷ n. A resistor of 0 Ω in parallel makes the total 0 Ω, because it is a short circuit.
What the formulas are not: they use the nominal values. Real resistors have a tolerance (1 % or 5 % for common types), and the total has at least that spread. Measured with a meter, a resistor that is still soldered in a circuit also reads the other parts of the circuit in parallel.
Worked examples
Two equal resistors. 100 Ω and 100 Ω. Parallel: (100 × 100) ÷ 200 = 50 Ω, half of one resistor. Series: 200 Ω.
| Resistors | Parallel | Series |
|---|---|---|
| 100 Ω, 100 Ω | 50 Ω | 200 Ω |
Three different resistors. 1 kΩ, 2.2 kΩ and 4.7 kΩ. Conductances: 1 ÷ 1000 + 1 ÷ 2200 + 1 ÷ 4700 = 0.001 + 0.000455 + 0.000213 = 0.001667 S, so the parallel total is 1 ÷ 0.001667 = 599.8 Ω, below the smallest value of 1 kΩ.
| Resistors | Parallel | Series |
|---|---|---|
| 1 kΩ, 2.2 kΩ, 4.7 kΩ | 599.8 Ω | 7.9 kΩ |
Four resistors. 330 Ω, 470 Ω, 680 Ω and 1 kΩ. Conductances: 0.003030 + 0.002128 + 0.001471 + 0.001000 = 0.007629 S, so the parallel total is 131.1 Ω.
| Resistors | Parallel | Series |
|---|---|---|
| 330 Ω, 470 Ω, 680 Ω, 1 kΩ | 131.1 Ω | 2.48 kΩ |
Measure it live
To check a network, connect a Bluetooth multimeter the app reads live, such as the OWON OW18B, set it to ohms and measure across the parallel node with the power off. Compare the reading with the calculated total.
The calculator in the app has preset formulas for Ohm's law and power, series and parallel, dividers, LED resistors, RC, dB and unit conversion, and a parallel operator for typing a sum directly. Cal Box fills it from your live reading and recent captures. Once you have the resistance, the Ohm's law calculator gives current and power.
What the app does here, and what it doesn't
| What it does | Plan |
|---|---|
| A calculator with SI prefix keys, engineering input such as 4k7 and a parallel operator. | Free |
| Presets for Ohm's law and power, series and parallel, dividers, LED resistors, RC, dB and unit conversion. | Free |
| Cal Box fills the calculator from your live reading and recent captures, and suggests Ohm's law. | Free |
Questions
How do I calculate resistors in parallel?
Add the reciprocals and take the reciprocal of the sum: 1 ÷ R = 1 ÷ R1 + 1 ÷ R2 + …. For two resistors, R = R1 × R2 ÷ (R1 + R2). 100 Ω and 100 Ω give 50 Ω.
Why is the parallel resistance lower than the smallest resistor?
Each resistor adds another path for the current, so the total conductance goes up and the resistance goes down. Two resistors of 1 kΩ and 10 kΩ in parallel give 909 Ω, less than 1 kΩ.
How do I add resistors in series?
Add the values: 1 kΩ and 2.2 kΩ in series are 3.2 kΩ. Choose the unit of each resistor in the calculator and read the series total below the parallel total.
Can I mix kΩ and Ω in the calculator?
Yes. Each row has its own unit box, so 470 Ω and 4.7 kΩ can be entered as they are written on the parts.
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