Enter your Filter Configuration, Resistance, Capacitance, and/or Inductance values into the Low Pass Filter Calculator to find your circuit's Cutoff Frequency (-3dB), along with the Time Constant and Angular Frequency — everything you need to understand where your filter starts rolling off the signal.
Cutoff Frequency (-3dB)
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Cutoff Frequency
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Time Constant
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Angular Frequency
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A low-pass filter is an electronic circuit that allows low-frequency signals to pass through while attenuating (reducing) high-frequency signals above a certain cutoff frequency. It's commonly used to remove noise and unwanted high-frequency components from signals.
For RC filters, the cutoff frequency is fc = 1/(2πRC). For RL filters, it's fc = R/(2πL). The cutoff frequency is where the output is -3dB (about 70.7%) of the input signal amplitude.
RC filters use a resistor and capacitor, are inexpensive and work well at higher frequencies. RL filters use a resistor and inductor, handle more current and are better for power applications, but inductors are larger and more expensive than capacitors.
For a 1 kHz RC filter with R=1kΩ, you'd need C≈0.159μF. For an RL filter with R=1kΩ, you'd need L≈159mH. Choose standard component values closest to your calculated requirements.
The -3dB point is the cutoff frequency where the output power is half the input power, or the output voltage is about 70.7% of the input voltage. It defines the boundary between the passband and stopband of the filter.
Passive filters (RC, RL, LC) don't need power supply, are simple and stable, but provide no gain. Active filters use op-amps, can provide gain and better control, but need power and are more complex to design.
The time constant τ (tau) is RC for RC filters and L/R for RL filters. It represents how quickly the filter responds to changes in input. The cutoff frequency is related by fc = 1/(2πτ).