Low Pass Filter Calculator
Find the cutoff frequency of an RC low-pass filter.
A low-pass filter passes low frequencies and attenuates high ones.
How the Math Works
The Low Pass Filter Calculator uses the formula fc = 1 ÷ (2π·R·C) to determine the cutoff frequency of an RC low-pass filter. This formula calculates the -3dB point where the filter begins to attenuate higher frequencies. The constant 2π (approximately 6.283) arises from the relationship between angular frequency and regular frequency. Resistance (R) is measured in ohms (Ω) and capacitance (C) in farads (F), producing a cutoff frequency (fc) in hertz (Hz). The calculation reveals how the product of R and C directly influences the filter's frequency response - larger values result in lower cutoff frequencies.
Practical Applications
To use this calculator practically, first identify your circuit's resistor value in ohms and capacitor value in farads (or convert from microfarads by multiplying by 10^-6). Enter these values into the calculator to instantly determine the cutoff frequency. For example, with a 10 Ω resistor and 100 µF capacitor, the calculator shows approximately 159 Hz cutoff. Engineers use this to design filters for audio equipment, signal conditioning, and noise reduction circuits. Select component values by rearranging the formula to solve for R or C when you know your desired cutoff frequency.
Day-to-Day Use
Understanding cutoff frequencies helps you make sense of everyday audio experiences. When adjusting bass settings on your home stereo, you're essentially controlling which low frequencies pass through to your speakers. The calculator explains why older telephone systems sounded 'tinny' - they filtered out most frequencies above 3 kHz. It also helps you troubleshoot why your smartphone might not pick up distant radio stations clearly, or why certain room acoustics make conversations difficult. By knowing how filters work in your headphones, speakers, and electronics, you can make more informed choices when purchasing audio equipment or setting up home entertainment systems.
Worked example
1 kΩ, 0.1 µF → about 1592 Hz.
FAQ
Low-pass vs high-pass?
Swapping the resistor and capacitor positions turns one into the other.