Low Pass Filter Calculator
Design a low-pass filter and calculate its response at any frequency.
About Low Pass Filter Calculator
A low-pass filter passes frequencies below cutoff and attenuates those above. At cutoff the output is 0.707 of input regardless of order, but the roll-off beyond it steepens with each additional stage. Anti-aliasing filters must attenuate everything above half the sampling rate, which usually requires third order or higher.
Formula
Low Pass Filter
Gain = 1 ÷ √(1 + (f/f_c)²) per order; f_c = 1 ÷ (2πRC)
- f_c
- Cutoff frequency
- order
- Cascaded stages, each multiplying the attenuation
Worked example
With the default values below, Low Pass Filter Calculator returns Cutoff Frequency of 994.718. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Resistanceminimum 0.01 ohm
- 1,600 ohm
- Capacitanceminimum 0 F
- 0 F
- Signal frequencyminimum 0.01 Hz
- 5,000 Hz
- Filter orderaccepts 1–8
- 1
Results
- Cutoff Frequency
- 994.718 Hz
- Gain at the Signal Frequency
- -14.194 dB
- Output as a Fraction of Input
- 0.19512
- Phase Shift
- -78.75 degrees
- Capacitance for a 1 kHz Cutoff
- 0.000000099472 F
Step by step
- 1Values used
- 2Low Pass Filter
- 3Cutoff Frequency= 994.718 Hz
- 4Gain at the Signal Frequency= -14.194 dB
- 5Output as a Fraction of Input= 0.19512
- 6Phase Shift= -78.75 degrees
- 7Capacitance for a 1 kHz Cutoff= 0.000000099472 F
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or fees or charges into account.
- Figures are rounded for display to 12 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Low Pass Filter calculated?
Gain = 1 ÷ √(1 + (f/f_c)²) per order; f_c = 1 ÷ (2πRC) A low-pass filter passes frequencies below cutoff and attenuates those above. At cutoff the output is 0.707 of input regardless of order, but the roll-off beyond it steepens with each additional stage.
Why does Low Pass Filter matter?
Anti-aliasing filters must attenuate everything above half the sampling rate, which usually requires third order or higher.
What values do I need to enter?
This calculator takes 4 inputs: Resistance, Capacitance, Signal frequency, Filter order. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.