⚡ Cutoff Frequency Calculator
Calculate filter cutoff frequency
Enter in Farads (e.g., 1e-6 for 1 microfarad)
How to Use This Calculator
Select Filter Type
Choose the type of filter: RC (resistor-capacitor), RL (resistor-inductor), or LC (inductor-capacitor). Each has a different cutoff frequency formula.
Enter Component Values
Input the values of the components used in your filter. For RC filters, enter resistance and capacitance. For RL filters, enter resistance and inductance. For LC filters, enter inductance and capacitance.
Calculate
Click the "Calculate Cutoff Frequency" button to get the -3dB cutoff frequency in Hertz (Hz). This is the frequency at which the filter's response drops to 70.7% of its maximum value.
Formula
RC Filter
fc = 1 / (2πRC)
Where R is resistance in Ohms and C is capacitance in Farads.
RL Filter
fc = R / (2πL)
Where R is resistance in Ohms and L is inductance in Henries.
LC Filter
fc = 1 / (2π√(LC))
Where L is inductance in Henries and C is capacitance in Farads.
Example Calculation (RC Filter):
For R = 1 kΩ (1000 Ω) and C = 1 μF (1 × 10⁻⁶ F):
fc = 1 / (2 × π × 1000 × 1 × 10⁻⁶)
fc = 1 / (6.28 × 10⁻³)
fc = 159.15 Hz
About Cutoff Frequency Calculator
The Cutoff Frequency Calculator determines the -3dB cutoff frequency of electronic filters (RC, RL, and LC). The cutoff frequency is the point at which the filter's output drops to 70.7% of its maximum value (or -3dB). This is a critical parameter in filter design for signal processing, audio systems, and communication circuits.
When to Use This Calculator
- Filter Design: Design high-pass, low-pass, and band-pass filters for specific frequency ranges
- Audio Systems: Calculate crossover frequencies for speaker systems and audio filters
- Signal Processing: Determine filter parameters for analog signal conditioning
- Circuit Analysis: Analyze existing filter circuits and verify component values
- RF Design: Design filters for radio frequency applications and communications
Why Use Our Calculator?
- ✅ Multiple Filter Types: Supports RC, RL, and LC filter calculations
- ✅ Accurate Results: Precise cutoff frequency calculations for filter design
- ✅ Easy to Use: Simple interface for quick filter parameter calculations
- ✅ Free Tool: No registration or payment required
- ✅ Educational: Learn the relationships between components and cutoff frequency
Common Applications
Audio Crossovers: Calculate crossover frequencies for speaker systems, where RC or LC filters separate audio signals into different frequency bands for woofers, midranges, and tweeters.
Signal Conditioning: Design filters for removing unwanted frequencies in sensor signals, data acquisition systems, and instrumentation applications.
Power Supply Filtering: Determine cutoff frequencies for power supply filters that remove AC ripple from DC power supplies, using RC or LC filters to smooth the output.
Tips for Best Results
- The -3dB point means the output power is half, and output voltage/current is 70.7% of maximum
- For RC low-pass filters, frequencies below fc pass with minimal attenuation
- For RC high-pass filters, frequencies above fc pass with minimal attenuation
- LC filters are commonly used for band-pass and band-stop filters
- Use consistent units: resistance in Ohms, capacitance in Farads, inductance in Henries
Frequently Asked Questions
What is the -3dB cutoff frequency?
The -3dB cutoff frequency is the frequency at which the filter's output drops to 70.7% of its maximum value. In terms of power, this represents a 50% reduction, which is -3 decibels (10×log₁₀(0.5) ≈ -3dB).
What's the difference between RC, RL, and LC filters?
RC filters use a resistor and capacitor, RL filters use a resistor and inductor, and LC filters use an inductor and capacitor. RC filters are most common for low-frequency applications, RL filters are less common, and LC filters are used for higher frequency applications and resonant circuits.
How do I design a filter for a specific cutoff frequency?
Rearrange the formula to solve for the component values. For example, for an RC filter: C = 1/(2πRfc). Choose a convenient resistor value, then calculate the required capacitance, or vice versa.
What's the difference between low-pass and high-pass filters?
A low-pass filter passes frequencies below the cutoff frequency and attenuates frequencies above it. A high-pass filter does the opposite - it passes frequencies above the cutoff and attenuates those below. The same formula applies; the filter configuration determines which frequencies pass.
Can I use this for band-pass filters?
LC filters are commonly used for band-pass filters, which have both a lower and upper cutoff frequency. For a simple LC resonant filter, the center frequency is at fc, with bandwidth determined by the quality factor (Q) of the circuit.
Why is the cutoff frequency important?
The cutoff frequency determines which frequencies are passed or blocked by the filter. It's crucial for separating signals, removing noise, and designing systems that operate in specific frequency ranges, such as audio crossovers, anti-aliasing filters, and communication systems.