Use this LC resonance calculator to solve for frequency (f), inductance (L), or capacitance (C) in a tuned oscillator or resonant tank circuit.
Formula used: f = 1 / (2π√(LC))
What is an LC oscillator?
An LC oscillator is an electronic circuit that generates a periodic signal using an inductor (L) and capacitor (C). Together they form a resonant tank that naturally oscillates at a specific frequency. This principle is used in RF transmitters, receivers, filters, local oscillators, signal generators, and many other analog designs.
The resonance frequency depends on both L and C, so changing either component shifts oscillation. That is why tuning capacitors and switched inductors are common in radio designs.
Core LC resonance formula
The ideal resonance frequency is:
f = 1 / (2π√(LC))
- f = frequency in hertz (Hz)
- L = inductance in henry (H)
- C = capacitance in farad (F)
Rearranged forms are:
L = 1 / ((2πf)2C)C = 1 / ((2πf)2L)
How to use this calculator
1) Choose what to solve
Select frequency, inductance, or capacitance from the dropdown.
2) Enter the other two values
Type known values and pick the correct units. The calculator converts everything internally to SI units before computing, which helps prevent unit mismatch errors.
3) Click Calculate
You get the result in both your selected unit and a convenient auto-scaled unit. The tool also shows resonant period
T = 1/f and angular frequency ω = 2πf when frequency is known.
Practical design notes (real-world behavior)
Ideal formulas are a starting point. Real circuits include losses and parasitics that shift resonance:
- Coil resistance (DCR) reduces Q and broadens bandwidth.
- Parasitic capacitance of the inductor and PCB can move the target frequency.
- Temperature drift in L and C can detune the oscillator.
- Active device loading (transistor/op-amp stage) may alter effective tank values.
- Tolerance stack-up from component variation can produce noticeable frequency spread.
In precision RF work, designers often simulate and then trim with variable capacitors or calibration routines.
Example calculations
Example A: Find resonant frequency
Suppose L = 10 µH and C = 100 pF.
Plugging values into the formula gives a resonance near 5.03 MHz.
Example B: Choose inductance for a target frequency
If you want f = 1 MHz with C = 1 nF, rearrange to solve L:
L = 1 / ((2πf)2C), yielding about 25.33 µH.
Example C: Choose capacitance for an RF tank
For f = 10 MHz and L = 1 µH, the needed capacitance is about
253 pF (ignoring parasitics).
Tips for better oscillator stability
- Use high-Q inductors and NP0/C0G capacitors when possible.
- Keep tank layout compact to minimize unwanted lead inductance/capacitance.
- Shield sensitive RF sections from nearby digital noise sources.
- Allow thermal warm-up before calibration in precision systems.
- Validate with a network analyzer or frequency counter on real hardware.
Frequently asked questions
Does this work for Colpitts and Hartley oscillators?
Yes, for first-pass resonance estimates. For detailed designs, include equivalent tank capacitance/inductance from the actual topology and active-device loading.
Why is measured frequency different from calculated frequency?
Usually because of parasitic capacitance, component tolerances, finite Q, and circuit loading. Real measurements are often a few percent off the ideal estimate.
Can I use this for filter center frequency too?
Yes, the same LC resonance relationship is commonly used for tuned filter sections and matching networks.