Last updated: Jul 29, 2024

RC Filter Calculator

Created by Krishna Nelaturu

Krishna Nelaturu

Krishna holds a Master's degree in Applied Mechanics and never shies away from asking questions and digging deeper. He has two years of experience in steel castings and a particular fascination for vehicle dynamics. For his thesis, Krishna developed a new optimization method to reduce squeak and rattle in premium cars. He is passionate about mathematics and physics and constantly wonders about our place in the Universe. He also loves stories and storytelling and hopes to write a book someday. See full profile

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Komal Rafay

A master's in Bioinformatics, with 3+ years of experience as a project manager. She has a vast experience of 7+ years in teaching Math, Computer science, and General Sciences, not only professionally but also to help out the children of the neighborhood. She is an enthusiastic reader with a thirst for knowledge who would even read the shampoo labels. As a side hustle that satisfies her love for art, she is a body art and henna expert. In her free time, you will find her reading books, writing short stories, playing with her pets, or experimenting with food while listening to some bouncy music. See full profile

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Table of contents

Calculating RC low-pass filter Calculating RC high-pass filter Calculating RC band-pass filter calculator How to use this online RC filter calculator?Other filter circuit calculators FAQs

This online RC filter calculator is a quick and easy tool to help you design an RC filter for low-pass or high-pass filter circuits. With just a couple of inputs, this tool will calculate the cutoff frequency for an RC filter circuit. Experts can even use this calculator to calculate RC band pass filter circuits!

A filter circuit is a circuit that will help you filter out undesired frequencies from the input signal. Depending on whether the circuit can remove high frequencies or low frequencies from the input signal, we call it a low-pass or a high-pass filter circuit. The following article briefly describes how to use an RC circuit as a low-pass or a high-pass filter.

Calculating RC low-pass filter

A low-pass filter calculator removes high-frequency noise from an input signal, allowing only low frequencies to pass through. The characteristic cutoff frequency is the frequency above which all signals are blocked from passage.

The Bode plot of a low-pass filter, showing the cutoff frequency above which input signals are blocked. — The Bode plot of a low-pass filter.

In practice, the drop in gain is not sharp - instead, the gain drops gradually. Hence, the cutoff frequency is the frequency at which the gain drops to -3 dB.

The RC filter circuit contains a resistor and a capacitor. A capacitor's impedance is inversely proportional to the signal frequency, while a resistor's impedance is independent of the signal frequency. For a low-pass filter, the capacitor is connected parallel to the load, while the resistor is in series with the load.

The bridge parallel to the load remains disconnected for low-frequency signals since the capacitor impedes any current from passing through. So, the low-frequency signals pass through the circuit to the output without deterrence.

On the other hand, high-frequency signals pass through the capacitor with negligible impedance, shorting the circuit before the output connection point. Thus, high frequencies are blocked from passing through.

The formula to calculate the cutoff frequency of the RC filter is:

f_c = \frac{1}{2 \pi RC}

where:

$f_c$ - The cutoff frequency of the RC filter;
$R$ - The resistance of the resistor; and
$C$ - The capacitance of the capacitor.

Calculating RC high-pass filter

A high-pass filter blocks low-frequency noise in the input signal, allowing only high-frequency signals to pass through.

The Bode plot of a high-pass filter, showing the cutoff frequency below which input signals are blocked. — The Bode plot of a high-pass filter.

Since the capacitor's impedance is inversely proportional to the signal frequency, it is connected in series with the load for a high-pass filter. This blocks low frequencies from reaching the load but allows high frequencies to pass unhindered.

Calculating the RC high pass filter's cutoff frequency uses the same formula we've seen in the previous section:

f_c = \frac{1}{2 \pi RC}

Calculating RC band-pass filter calculator

A band-pass filter lets a specific range of frequencies through while blocking the others. It is a circuit that combines a low-pass and high-pass filter. To calculate an RC band-pass filter, follow these steps:

Calculate an RC low-pass filter that blocks all frequencies below the desired range.
Calculate an RC high-pass filter that blocks all frequencies above the desired range.
Use them in the appropriate combination.

How to use this online RC filter calculator?

Our RC filter calculator is simple to use:

Input the resistance of the resistor.
Enter the capacitance of the capacitor.
The RC filter calculator will automatically determine the cutoff frequency of the filter circuit.

If you're designing a circuit with a cutoff frequency in mind, you can enter the cutoff frequency and either the resistance or the capacitance to find the remaining variable. This online RC filter calculator is robust - play around till you arrive at satisfactory values.

Other filter circuit calculators

We have other filter circuit calculators for you to explore:

FAQs

How do you calculate the cutoff frequency of an RC filter?

To calculate the cutoff frequency of an RC filter circuit, follow these steps:

Multiply the resistance of the resistor (in Ohms) with the capacitance of the capacitor (in Farads).
Multiply the result with 2π.
Take the reciprocal of this product to find the cutoff frequency of the RC filter.

What inductor do I need for a 1 kHz RC high-pass filter?

To design an RC high-pass filter with a 1 kHz cutoff frequency using a standard capacitor of 47 nF, follow these steps:

Multiply the cutoff frequency (in Hz) with the capacitance (in Farads):
1000 Hz × 47×10^-9 F = 47×10^-6
Multiply this result with 2π and take the reciprocal of the product to obtain the resistance (in Ohms):
R = 1/(2π × 47×10^-6) = 3.386×10³ Ω = 3.386 kΩ
Verify this result using our RC filter calculator.