In series
Rtotal = R1 + R2 + R3 + ...
In Parallel
Rtotal = 1 / (1/R1 + 1/R2 + 1/R3 + ...)
This tool calculates the equivalent resistance of several resistors connected either in series or in parallel. Enter each resistor value with its unit (Ω, kΩ, or MΩ), and the calculator will apply the correct formula automatically.
When resistors are connected end-to-end (in series), their resistances add up:
Req = R₁ + R₂ + ... + Rₙ
The total resistance is always greater than any individual resistor.
When resistors share the same two nodes (in parallel), the reciprocal of the total resistance equals the sum of the reciprocals:
1/Req = 1/R₁ + 1/R₂ + ... + 1/Rₙ
The total resistance is always less than the smallest individual resistor.
Ohm (Ω)
Kiloohm (kΩ) = 1,000 Ω
Megaohm (MΩ) = 1,000,000 Ω
You can mix units—e.g., enter "1k", "470", and "2.2M"—and the calculator will convert them correctly.
Voltage divider circuits: Combine two resistors to scale down a voltage.
Current limiting: Use a series resistor to protect LEDs or sensors.
Pull-up/pull-down networks: Set default logic levels in digital circuits.
Impedance matching: Adjust total resistance for signal integrity.
Educational labs: Teach Ohm’s Law and Kirchhoff’s laws.
| Configuration | Resistor Values | Equivalent Resistance |
|---|---|---|
| Series | 100 Ω, 200 Ω, 300 Ω | 600 Ω |
| Parallel | 1 kΩ, 1 kΩ | 500 Ω |
| Parallel | 10 kΩ, 10 kΩ, 10 kΩ | ≈3.33 kΩ |
Capacitor Sum Calculator – for series/parallel capacitance
Voltage Divider Calculator – design precise output voltages
Ohm’s Law Calculator – compute voltage, current, resistance, or power
The calculator will typically ignore non-numeric inputs or show an error. Always use numbers followed by optional unit symbols (e.g., 4.7k, 100, 2M).
Because current has multiple paths to flow through. More paths mean less overall opposition to current—hence lower total resistance.
Yes. Most implementations allow you to add as many resistors as needed—the formulas work for any number of components.
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