AC foundations
Inductive reactance
- where
- inductive reactance (Ω)
- frequency (Hz)
- inductance (H)
Explain this equation
Works out how strongly an inductor opposes alternating current at a given frequency. Used for chokes, coils and motor windings.
Xₗ is the inductive reactance in ohms. f is the supply frequency and L is the inductance in henries. 2πf is the angular frequency in radians per second.
An inductor fights changes in current. The faster the current changes, the harder it fights, so reactance rises in step with both frequency and inductance. The 2π converts cycles per second into radians per second.
Sense check: 0.1 H at 50 Hz is about 31.4 Ω. Double the frequency and Xₗ doubles. On DC (zero frequency) it is zero.
Watch out: make sure the unit selector matches your value, mH or H. A thousand-fold error is easy to make.
An ideal inductor opposes changes in current. In sinusoidal steady state its reactance increases with frequency and inductance.
Reactance is not resistance: an ideal inductor stores and returns energy rather than dissipating average real power.
Enter your values to see the result.
Common mistake
Using mH without conversion to H.
Limits
Sinusoidal steady state, linear inductor.
Sources
The tools calculate the displayed equation. They do not automatically choose cable sizes, approve installations, supply current regulatory tables, certify equipment or replace inspection and testing.