Resonant Frequency Calculator (LC Tank)
Where L is inductance in henries (H) and C is capacitance in farads (F).
What Is an LC Oscillator?
An LC oscillator is an electronic circuit that uses an inductor (L) and a capacitor (C) to create a repeating signal at a natural resonant frequency. The inductor stores energy in a magnetic field, while the capacitor stores energy in an electric field. Energy moves back and forth between these two components, creating oscillation.
This behavior is the foundation for many practical systems, including RF transmitters, local oscillators, filters, and tuned amplifiers. Whether you are designing a simple hobby radio or doing serious frequency planning, quickly calculating resonance is a core skill.
How the Formula Works
The resonant frequency for an ideal LC tank circuit is:
f = 1 / (2π√(LC))
- f = frequency in hertz (Hz)
- L = inductance in henries (H)
- C = capacitance in farads (F)
From the equation, increasing either L or C lowers frequency, and decreasing them raises frequency. This is why small changes in component values can noticeably shift oscillator performance.
How to Use This LC Oscillator Frequency Calculator
Step-by-step
- Enter your inductance value and choose its unit (H, mH, µH, nH, or pH).
- Enter your capacitance value and choose its unit (F, mF, µF, nF, or pF).
- Select your preferred output frequency unit (Hz, kHz, MHz, GHz).
- Click Calculate Frequency to see resonant frequency, angular frequency, and period.
The calculator handles all unit conversion for you, so you can work with real-world component values without manual conversion errors.
Example Calculations
Example 1: 10 µH and 100 nF
This common pair yields a resonant frequency around 159 kHz. It is useful in lower-frequency tuned circuits and analog signal experiments.
Example 2: 1 µH and 100 pF
This combination moves resonance into the MHz range, often used in RF front-end prototypes and compact tuned stages.
Example 3: 220 nH and 22 pF
Smaller values push resonance significantly higher and are typical in high-frequency oscillator networks where parasitics become important.
Practical Design Notes
The ideal formula is a great starting point, but real circuits include non-ideal effects. Keep these in mind:
- Component tolerance: ±1%, ±5%, or ±10% parts can shift your actual frequency.
- Parasitic capacitance: PCB traces, transistor junctions, and probes add extra C.
- Inductor Q factor: Low-Q inductors reduce stability and increase losses.
- Temperature drift: L and C values can vary with ambient temperature.
- Loading effects: Connected stages can pull frequency away from the ideal result.
Common Mistakes to Avoid
- Mixing units (e.g., entering µH and assuming H).
- Forgetting that capacitance in pF is very small in farads.
- Using zero or negative values (not physically valid for this equation).
- Ignoring stray capacitance in high-frequency layouts.
FAQ
Is this calculator for series or parallel LC circuits?
The resonance equation used here applies to both ideal series and parallel LC tanks. Real behavior differs with loading and loss, but the ideal resonant frequency is the same.
What if I need more precision?
Start with this calculator for first-pass design, then validate using SPICE simulation or bench measurements with actual components and layout parasitics included.
Can I use this for Colpitts or Hartley oscillators?
Yes, as long as you compute the equivalent tank inductance and capacitance seen by the oscillator core. The resonance estimate is still useful for target frequency planning.
Final Thoughts
A good LC oscillator design begins with a reliable frequency estimate. Use the calculator above to move quickly from component values to resonance, then refine with practical considerations like tolerance, Q, and layout effects. It is one of the simplest and most powerful tools in analog and RF design work.