Cutoff Frequency Calculator
Calculate the -3dB cutoff frequency for RC and RL filter circuits
Calculate Cutoff Frequency
Select the type of filter circuit you want to analyze
Select which parameter you want to calculate. The others will be used as inputs.
Resistance value of the resistor component
Capacitance value of the capacitor component
Calculation Results
Formula used: fc = 1 / (2π × R × C)
Circuit Type: RC Filter (Low-Pass/High-Pass)
At the cutoff frequency, the output power is reduced to 50% (-3dB) of the input power
Example Calculations
RC Low-Pass Filter
Resistance: 10 kΩ
Capacitance: 25 nF
Calculation: fc = 1 / (2π × 10,000 × 25×10⁻⁹)
Cutoff Frequency: 636.6 Hz
Application: Audio filtering, anti-aliasing
RL High-Pass Filter
Resistance: 1 kΩ
Inductance: 10 mH
Calculation: fc = 1,000 / (2π × 0.01)
Cutoff Frequency: 15.9 kHz
Application: Radio frequency filtering
Filter Types
Low-Pass Filter
Passes frequencies below fc
RC configuration
High-Pass Filter
Passes frequencies above fc
RC or RL configuration
Key Concepts
-3dB Point
Power reduced to 50%
Voltage ratio = 0.707
Corner Frequency
Transition point between
pass and stop bands
Reactance
Frequency-dependent
impedance of L and C
Understanding Cutoff Frequency
What is Cutoff Frequency?
The cutoff frequency (also called corner frequency) is the frequency at which the output signal power drops to half (-3dB) of its maximum value. At this point, the voltage gain drops to approximately 0.707 (1/√2) of the maximum.
Why -3dB?
The -3dB point is chosen because it represents a power reduction to exactly half. In decibels: -3dB = 20 × log₁₀(0.707) = 10 × log₁₀(0.5), making it a convenient reference point for defining filter characteristics.
Filter Formulas
RC Filter: fc = 1/(2π×R×C)
RL Filter: fc = R/(2π×L)
fc: Cutoff frequency (Hz)
R: Resistance (Ω)
C: Capacitance (F)
L: Inductance (H)
Applications
- •Audio processing and speaker crossovers
- •Anti-aliasing in digital systems
- •Power supply noise filtering
- •Radio frequency signal processing