Impedance is the total opposition an AC circuit offers to current, in ohms: Z = √(R² + (XL − XC)²). Inductive reactance rises with frequency and capacitive reactance falls, so the same parts have a different impedance at 50 Hz and 60 Hz.
When a resistor, inductor and capacitor sit in series, the total opposition an AC supply sees is the impedance. Capacitive reactance falls as frequency rises and inductive reactance grows, so the same parts give different answers on 50 Hz and 60 Hz. Pick your country to load the local frequency and voltage. Enter only a capacitor to get its reactance.
Result
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Formula
- XC = 1 ÷ (2π × f × C)
- XL = 2π × f × L
- Z = √(R² + (XL − XC)²)
- Phase angle φ = arctan((XL − XC) ÷ R), power factor = R ÷ Z
How to use it
- Pick your country to load frequency and voltage.
- Enter R, L and C. Leave any part you do not have empty.
- Read XC, XL, Z and current. A negative phase angle means the circuit is capacitive, positive means inductive.
This is an estimating tool. Follow your local electrical code and have a qualified electrician confirm any real installation.
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Frequently asked questions
What is impedance?
In DC only resistance matters. In AC, inductors and capacitors also oppose current, and combining resistance with both reactances gives the impedance. It sets how much current flows at a given voltage: I = V ÷ Z.
How do you calculate capacitive reactance?
XC = 1 ÷ (2π × f × C). Higher frequency or larger capacitance means lower reactance: 100 μF is about 26.5 Ω at 60 Hz and 31.8 Ω at 50 Hz.
What does a positive or negative phase angle mean?
Positive means inductive reactance wins and current lags voltage. Negative means the circuit is capacitive and current leads voltage. The power factor is R ÷ Z.
Is impedance measured in the same unit as resistance?
Yes, both are in ohms, but impedance changes with frequency and resistance does not, so note the test frequency of any meter reading.
