General EE Utilities
RC / LC FILTER CALCULATOR
Calculate cutoff frequency, impedance, and Q factor for RC and LC low-pass and high-pass filters. Includes Bode plot visualization.
Calculate the cutoff frequency for RC and LC filters in low-pass or high-pass configuration. Enter component values to see the −3dB point, time constant, impedance, and an interactive Bode magnitude plot.
Filter Type
Configuration
Component Values
Results
Cutoff Frequency (−3dB)
ωc = 1.000e+3 rad/s
Time Constant (τ)
1.000 ms
XC at fc
10.00 kΩ
Rise Time (10-90%)
2.200 ms
Rolloff
−20 dB/dec
Circuit Diagram
Frequency Response (Bode Plot)
RC / LC Filter Calculator Results
Generated by calpak-usa.com/Resources/RC-LC-Filter-Calculator
| Filter Type | RC low-pass |
| Resistance | 10 kΩ |
| Capacitance | 100 nF |
| Cutoff Frequency | 159.15 Hz |
| Time Constant | 1.000 ms |
| Impedance at fc | 10.00 kΩ |
For reference only. Ideal component model — does not account for parasitic effects.
Formulas Used
The calculator applies first-order RC and ideal second-order LC relationships for cutoff frequency and derived response values.
\[f_{c,RC} = \frac{1}{2\pi RC}\]
\[\tau = RC\]
\[f_{c,LC} = \frac{1}{2\pi\sqrt{(LC)}}\]
\[Z_{0,LC} = \sqrt{\left(\frac{L}{C}\right)}\]
\[\omega_c = 2\pi f_c\]
R in ohms
C in farads
L in henries. fc is the −3 dB cutoff frequency.
Understanding RC and LC Filter Circuits
Passive filters are fundamental building blocks in electronics, used to pass or reject specific frequency ranges. The simplest forms use just two components: a resistor paired with a capacitor (RC filter) or an inductor paired with a capacitor (LC filter). Despite their simplicity, these circuits appear everywhere — from audio processing and power supply decoupling to RF signal conditioning and sensor interfaces.
An RC low-pass filter passes low frequencies while attenuating high frequencies. At the cutoff frequency fc = 1/(2πRC), the output is −3dB (approximately 70.7%) of the input. Above the cutoff, attenuation increases at −20 dB per decade — meaning each 10× increase in frequency reduces the signal by a factor of 10. The time constant τ = RC determines how quickly the filter responds to step inputs.
LC filters offer steeper rolloff than RC filters: −40 dB per decade for a second-order design. This makes them preferred for applications requiring sharper frequency separation, such as RF front-ends and switching power supply output filtering. However, LC filters can exhibit resonance at the cutoff frequency, creating a gain peak that must be managed with proper damping.
For aerospace and defense applications, filter design must account for component tolerance, temperature drift, and aging effects. Military-grade capacitors and inductors are specified with tighter tolerances and wider operating temperature ranges. Calpak USA's engineering team can help design and validate filter circuits for MIL-spec and space-grade applications. Contact us for design support.
Quick Reference: Common Filter Cutoff Frequencies
RC low-pass filter configurations
| Application | R | C | fc |
|---|---|---|---|
| Audio anti-alias | 10 kΩ | 820 pF | 19.4 kHz |
| Power supply decoupling | 10 Ω | 100 nF | 159 kHz |
| Sensor smoothing | 100 kΩ | 100 nF | 15.9 Hz |
| RF interference filter | 1 kΩ | 1 nF | 159 kHz |
Ideal values assuming perfect components. Real-world performance varies with component tolerance, parasitic capacitance/inductance, and PCB layout.
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