LC Filter Calculator
Table of contents
What are filter circuits?Calculating LC low pass filterCalculating LC high pass filterCalculating LC bandpass filterUsing this LC filter calculatorOther filter calculatorsFAQsOur LC filter calculator will help you calculate an LC filter circuit's cutoff frequency. Whether you're designing a lowpass or a highpass filter, this calculator will prove helpful. If you know what you're doing, you can calculate an LC band pass filter circuit with this tool!
In the following article, we shall look at what filter circuits are and how to calculate the cutoff frequency of LC filter circuits.
What are filter circuits?
A filter circuit is an electronic circuit designed to "filter" out some frequencies from an input signal. A filter circuit that allows low frequencies to pass while blocking high frequencies is a lowpass filter circuit. On the other hand, a circuit that deters low frequencies and allows high frequencies to pass is a highpass filter circuit.
A characteristic of a filter circuit is the cutoff frequency. In a lowpass filter, it is the frequency above which all input signals are blocked. An input signal below this cutoff frequency passes through this circuit.
Theoretically, the transition near the cutoff frequency must be sharp, as shown by the blue line in the plot above. But in practice, this drop in gain is gradual. As such, the cutoff frequency of a filter circuit is defined as the frequency at which the gain has dropped to 3 dB.
Like in a lowpass filter, the cutoff frequency of a highpass filter is the frequency below which all input signals are blocked. In other words, it is the frequency above which the input signals can pass through a highpass filter undeterred.
Calculating LC low pass filter
An LC filter is a secondorder filter circuit because it has both an inductor and a capacitor, whose impedance depends on the signal's frequency. As such, it reacts faster to a signal frequency and has twice the frequency slope (also known as frequency rolloff) in the Bode plot compared to a passive filter like RC or RL.
A lowpass LC filter circuit has an inductor connected in series with the load and a capacitor connected in parallel. An inductor's impedance is directly proportional to a signal's frequency, while a capacitor's impedance is inversely proportional. So, low frequencies pass through the circuit without hindrance, while high frequencies cannot.
The formula to calculate the LC lowpass filter's cutoff frequency is:
where:

$f_c$ — The cutoff frequency of the LC filter circuit;

$L$ — The inductance of the inductor; and

$C$ — The capacitance of the capacitor.
Calculating LC high pass filter
A secondorder highpass LC filter has a capacitor connected in series with the load and the inductor connected in parallel. Because a capacitor's impedance is inversely proportional to the signal frequency, whereas an inductor's impedance is directly proportional to it, the circuit will block lowfrequency signals, allowing highfrequencies to pass through it.
The formula to calculate the LC highpass filter's cutoff frequency:
Calculating LC bandpass filter
A bandpass filter is a circuit that allows a desired band of frequencies to pass through, blocking the rest. It is a combination of a lowpass and highpass filter circuit. So, to calculate an LC bandpass filter, you must:

Calculate an LC lowpass filter that blocks all frequencies below the desired range.

Calculate an LC highpass filter that blocks all frequencies above the desired range.

Use them in an appropriate combination.
Using this LC filter calculator
This LC filter calculator will be handy when designing either a lowpass or a highpass filter:

Enter the inductance of the inductor in your desired unit.

Provide the capacitance of the capacitor in a unit of your choice.

The tool will instantly calculate the LC filter's cutoff frequency.
Alternatively, you can use this LC filter calculator to determine the LC filter components required to achieve the desired cutoff frequency:

Input the target cutoff frequency.

Enter either the inductance or the capacitanceand our LC filter calculator will determine the remaining value.
Other filter calculators
Did you find our LC filter calculator helpful? We have more filter calculators for you to try next:
How do you calculate the cutoff frequency of an LC filter circuit?
To calculate the cutoff frequency of an LC filter circuit, follow these steps:

Multiply the inductance in Henries (H) with the capacitance in Farads (F).

Take the square root of this product.

Multiply the result with 2π.

Take the reciprocal of this product to obtain the cutoff frequency.
Our LC filter calculator will help you calculate the cutoff frequency of an LC filter without any hassle!
What inductor do I need for a 1 kHz LC low pass filter?
Using a standard capacitor of 47 nF, you need an inductor with an inductance of 0.5389 H or 538.9 mH to have a cutoff frequency of 1 kHz. To calculate this answer, follow these steps:

Multiply the capacitance with the square of the cutoff frequency:
(1×10^{3} Hz)^{2} × 47×10^{9} F = 47×10^{3}

Multiply this result with 4π^{2}:
4π^{2} × 47×10^{3} ≈ 1.855485

Take the reciprocal of this value to obtain the inductance:
1/1.855485 ≈ 0.5389 H or 538.9 mH