This passive RC low pass filter calculator calculates the cutoff frequency point of the low pass filter,
based on the values of the resistor, R, and the capacitor, C,
of the circuit, according to the formula **fc= 1/(2πRC)**.

To use this calculator, all a user must do is enter any values into any of the 2 fields, and the calculator will calculate the third field. This calculator allows a user to select the magnitude of the units of the capacitor, including picofarads (pF), nanofarads (nF), microfarads (µF), and farads (F), as well as the unit for resistance and frequency. After 2 values are entered in, the user clicks the 'Calculate' button, and the result is automatically computed. The resultant value of the cutoff frequency calculated is in unit hertz (Hz) for frequency, farads and microfarads for the capacitor, and ohms(Ω) for the resistor.

An RC low pass filter is a filter circuit, composed of a resistor and a capacitor, which passes low-frequency signals and blocks high frequency signals. When a resistor is placed in series with the power source and a capacitor is placed in parallel to that same power source, as shown in the diagram circuit above, this type of circuit forms a low pass filter. It forms a low pass filter because of the reactive properties of a capacitor. A capacitor is a reactive device. This means that the resistance that it offers to a signal changes depending on the frequency of the signal. Capacitors are reactive devices that offer very high resistance, or impedance, to low frequency signals. Conversely, they offer lower resistance as the frequency of the signal increases. Thus, a capacitor offers very low impedance to a very high frequency signal. Because they offer low impedance to high-frequency signals, high frequency signals normally go through, as they represent a low-impedance path. Remember that current always takes the path of least resistance. So high-frequency signals normally take the capacitor path, while low-frequency signals don't; they go through to output.

When we calculate the cut-off frequency of the low pass filter, which is what this calculator does, we're calculating the point in the frequency response of the filter, where the gain has dropped by 3dB. Low pass filters pass low frequencies with high gain until it reaches a point in the frequency response curve where it no longer can pass out frequencies with as much gain. As the frequency gets higher, the signals get attenuated. The point at which the low pass filter can longer produce full gain and has dropped the gain by 3dB is referred to as the cutoff frequency. The cutoff frequency is the point where we know that the filter produces 0.7071V of the peak voltage gain. This is why it's crucial and why just knowing the cutoff frequency where the low-pass filter ends. At this frequency, signals begin attenuating greatly, and no longer pass signals with high very much gain.

As you can see in the above diagram, the low pass filter produces its full gain for low frequency signals and then begins producing lower gain signals.
At the cutoff frequency, there is a 3dB reduction in gain. And as the frequency increases, the gain reduces even more, until it's essentially 0.