RC Low Pass / High Pass Filter Calculator

RC Low Pass / High Pass Filter Calculator supports engineering calculations with transparent assumptions, practical result interpretation, and links to next-step technical resources.

Filter Visualization

Formula

fc = 1 / (2πRC)

|H(jω)| = 1 / √(1 + (f/fc)²)

φ = -atan(f/fc)

τ = R × C

First-order RC response rolls off at 20 dB/decade beyond cutoff.

Simplified RC Circuit

Magnitude Response (Bode)

Enter R and C to render dynamic filter response.

Inputs & Outputs

Resistance (R)

Capacitance (C)

Analysis Frequency (optional)

Input Amplitude Vin (optional)

Cutoff Frequency—

Time Constant (τ)—

R / C—

Point Response

Enter analysis frequency to compute gain and phase at a specific point.

RC Filter Fundamentals

Low-pass and high-pass filters share the same cutoff equation but invert what they preserve. Low-pass keeps slower components; high-pass rejects DC and emphasizes changes.

Low-Pass View

Passband at frequencies below fc.

Roll-off starts around fc with -20 dB/decade slope.

Typical use: sensor smoothing, anti-alias front-end conditioning.

High-Pass View

Rejects DC and low-frequency drift below fc.

Passes higher-frequency content with the same first-order slope.

Typical use: AC coupling, offset removal, edge emphasis.

Normalized Response Reference

Quick lookup values relative to cutoff frequency for first-order RC magnitude and phase behavior.

Frequency Ratio	Low-Pass Gain	High-Pass Gain	Phase Shift (LP / HP)
f = 0.1 × fc	≈ -0.04 dB (near passband)	≈ -20.04 dB (strong attenuation)	LP ≈ -5.7°, HP ≈ +84.3°
f = fc	-3.01 dB	-3.01 dB	LP = -45°, HP = +45°
f = 10 × fc	≈ -20.04 dB	≈ -0.04 dB	LP ≈ -84.3°, HP ≈ +5.7°

Filter Design Matrix

Select topology and component strategy from functional targets, then verify tolerance and loading impact.

Scenario	Objective	Recommendation	Critical Checks
Sensor anti-noise conditioning	Suppress high-frequency noise while preserving low-speed signal content	Use low-pass mode and place cutoff 3x to 10x above highest required signal component.	Signal delay, ADC sampling interaction, source impedance effects
Edge/pulse coupling into control logic	Block DC offset and pass fast transitions	Use high-pass mode with cutoff below minimum pulse-repetition frequency.	Baseline restoration, pulse droop, input bias network compatibility
EMI-aware analog front-end	Shape bandwidth to reduce conducted and radiated susceptibility	Select RC values with layout parasitics considered, then verify measured corner frequency.	Parasitic C/L, tolerance drift, thermal stability