UseCalcPro
Home
MathFinanceHealthConstructionAutoPetsGardenCraftsFood & BrewingTools
Blog
  1. Home
  2. Tools

RC Filter Calculator

Low-pass and high-pass filter cutoff frequency

Cutoff Frequency

159.15 Hz

Type

Low-Pass

e.g. 0.0000001 = 100nF

Cutoff Frequency

159.15 Hz

Filter

Low-Pass

Time Const

1.000 ms

Formula: fc = 1 / (2πRC)

-3dB at cutoff, -20dB/decade rolloff

Example Calculations

1Low-pass: 10kΩ + 100nF

Inputs

R10,000 Ω
C100 nF (0.0000001 F)
TypeLow-Pass

Result

Cutoff Frequency159.15 Hz
Time Constant1.000 ms

fc = 1/(2π×10000×0.0000001) = 1/(0.00628) = 159.15Hz. τ = 10000×0.0000001 = 1ms.

2Find R for 1kHz with 100nF

Inputs

Target fc1,000 Hz
C100 nF (0.0000001 F)

Result

Required R1,592 Ω

R = 1/(2π×1000×0.0000001) = 1/(0.000628) = 1,592Ω. Use 1.5kΩ or 1.6kΩ standard value.

Frequently Asked Questions

Q

How do I calculate RC filter cutoff frequency?

fc = 1/(2πRC). For R=10kΩ and C=100nF: fc = 1/(2π×10000×0.0000001) = 159.15Hz. This is the -3dB point where output is 70.7% of input.

  • fc = 1/(2πRC)
  • 10kΩ + 100nF = 159Hz
  • 10kΩ + 10nF = 1.59kHz
  • -3dB at cutoff: output = 70.7% of input
RCCutoff FrequencyUse Case
10kΩ100nF159 HzAudio sub-bass
10kΩ10nF1.59 kHzAudio treble
1kΩ100nF1.59 kHzSignal filtering
100kΩ1nF1.59 kHzHigh-impedance
Q

What is the difference between low-pass and high-pass?

Low-pass passes frequencies below fc and attenuates above. High-pass passes above fc and blocks below. Same formula, different capacitor placement in the circuit.

  • Low-pass: C to ground after R (output across C)
  • High-pass: C in series before R (output across R)
  • Same fc formula: 1/(2πRC)
  • Both attenuate at 20dB/decade (1st order)
Q

What is the rolloff of a 1st-order RC filter?

A single RC filter has -20dB/decade (6dB/octave) rolloff. This means for every 10x frequency increase past fc, the signal drops by 20dB (factor of 10 in voltage).

  • -20dB/decade = -6dB/octave
  • At fc: -3dB (70.7% voltage)
  • At 10×fc: -20dB (10% voltage)
  • For steeper rolloff: cascade multiple stages
Q

How do I design an anti-aliasing filter for ADC?

Set cutoff at half the sampling rate (Nyquist). For 44.1kHz sampling: fc = 22.05kHz. A 2nd-order filter (-40dB/decade) is minimum; 4th order preferred for audio.

  • fc = sample_rate / 2
  • 44.1kHz ADC: fc = 22kHz
  • Single RC: only -20dB/decade (weak)
  • Use active filter or multiple RC stages

Related Calculators

Capacitor Calculator

RC timing, energy, combinations

555 Timer Calculator

Astable and monostable timing

Speaker Crossover Calculator

Audio crossover design

Kayak Paddle Length Calculator

Calculate your ideal kayak paddle length by height, kayak width, torso length, and stroke style. Low angle touring vs high angle performance paddle sizing.

Subwoofer Box Calculator

Subwoofer box calculator for sealed and ported enclosures. Calculate box volume, port length, and tuning frequency for 10, 12, and 15 inch subwoofers.

No-Buy Challenge Calculator 2026 — Savings

Calculate how much you'll save with a no-buy or low-buy challenge in 2026. Enter your actual discretionary spending to see your total savings potential.

Related Resources

Capacitor Calculator

RC timing and capacitor combinations

555 Timer Calculator

Timing circuits with R and C

Speaker Crossover Calculator

Audio crossover component values

More Utility Calculators

Electronics, outdoor, and everyday tools

View All Tools

Last Updated: Mar 20, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

UseCalcPro
FinanceHealthMath

© 2026 UseCalcPro