Case 1
- Resistance R (Ω)
- 3Ω
- Net reactance X (Ω)
- 4Ω
5.000000Ω
Open with these valuesImpedance Calculator
5.000000Ω
Result: 5.000000 ΩResistance and reactance do not simply add up. They sit at right angles to each other, so 3 Ω of resistance with 4 Ω of net reactance make 5 Ω of impedance, not 7 Ω. A negative reactance means the circuit is capacitive, and it gives the same magnitude as the equal positive value.
The numbers at a glance
Held fixed: Resistance R (Ω) 3.000 Ω.
| Net reactance X (Ω) (Ω) | Result (Ω) |
|---|---|
| 0.000 | 3.000000 |
| 1.000 | 3.162278 |
| 2.000 | 3.605551 |
| 3.000 | 4.242641 |
| 4.000Your value | 5.000000 |
| 5.000 | 5.830952 |
| 6.000 | 6.708204 |
| 7.000 | 7.615773 |
| 8.000 | 8.544004 |
Worked examples
Case 2
- Resistance R (Ω)
- 60Ω
- Net reactance X (Ω)
- 80Ω
100.000000Ω
Open with these valuesCase 3
- Resistance R (Ω)
- 100Ω
- Net reactance X (Ω)
- -200Ω
223.606798Ω
Open with these valuesHow it's calculated
|Z| = √(R² + X²)
- StepEnter the resistance in ohms — the opposition that does not change with frequency.
- StepEnter the net reactance X = X_L − X_C, negative when the circuit is capacitive.
- ResultRead the impedance magnitude in ohms; the phase angle is a separate quantity.
Reference table
| R, X | Circuit | |Z| in Ω |
|---|---|---|
| 0, 5 | Purely reactive | 5 |
| 3, 4 | Inductive | 5 |
| 5, 0 | Purely resistive | 5 |
| 10, −10 | Capacitive | 14.142136 |
| 60, 80 | Inductive | 100 |
| 100, −200 | Capacitive | 223.606798 |
Questions
How do I calculate impedance?
For a series RLC circuit, take the square root of the sum of the squares of the resistance and the net reactance: |Z| = √(R² + X²). So 3 Ω of resistance with 4 Ω of net reactance give √25 = 5 Ω.
What is impedance?
Impedance is the total opposition a circuit presents to an alternating current. It combines resistance, which does not depend on frequency, with reactance, which does. Like resistance it is measured in ohms, but it applies to AC rather than steady direct current.
What is the difference between impedance and resistance?
Resistance opposes current in any circuit and dissipates energy as heat, while reactance is the extra opposition from inductors and capacitors that stores energy instead. Impedance is the combination of both. For a pure resistor with no reactance, impedance equals resistance.
Can the reactance be negative?
Yes, and a negative net reactance means the circuit is capacitive. Because the reactance is squared, a negative value gives the same impedance magnitude as the equal positive one. What differs is the phase angle, which this calculator does not report.
What units does impedance use?
Impedance, resistance and reactance are all measured in ohms. Make sure the reactance is worked out at your operating frequency, because reactance changes with frequency.
Sources and last check
Information, not professional advice.