# Low-Pass Filter Calculator

URL: https://speedycalculator.com/calculators/physics/low-pass-filter/
Last updated: 2026-10-30

> The low-pass filter calculator finds the cutoff frequency of a passive RC or RL low-pass filter, or the cutoff and gain of an active inverting or non-inverting op-amp low-pass filter.

## Inputs

- Filter type
- Resistance R (R₁ for inverting) (kΩ, Ω, MΩ)
- Capacitance C (nF, µF, pF, mF, F)
- Inductance L (mH, µH, nH, H)
- Feedback resistor R₂ (kΩ, Ω, MΩ)
- Ground resistor R₁ (non-inverting gain) (kΩ, Ω, MΩ)

## Results

- Cutoff frequency f_c
- Passband gain
- Passband gain in dB

## Formula

```
RC: f_c = 1/(2πRC) · RL: f_c = R/(2πL) · Inverting op-amp: f_c = 1/(2πR₂C), gain = −R₂/R₁ · Non-inverting: f_c = 1/(2πRC), gain = 1 + R₂/R₁
```

## Explanation

A low-pass filter passes slow changes and blocks fast ones: smoothing sensor readings, removing hiss, or preventing aliasing before an analogue-to-digital converter.

### How to use the Low-Pass Filter Calculator

- **Filter type**
- **Resistance R (R₁ for inverting)**
- **Capacitance C**
- **Inductance L**
- **Feedback resistor R₂**
- **Ground resistor R₁ (non-inverting gain)**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Choose the filter type and enter the component values.

### Inputs explained

FieldWhat to enterFilter typeChoose one: Passive RC, Passive RL, Active inverting op-amp, Active non-inverting op-ampResistance R (R₁ for inverting)Units: kΩ, Ω, MΩCapacitance CUnits: nF, µF, pF, mF, FInductance LUnits: mH, µH, nH, HFeedback resistor R₂Units: kΩ, Ω, MΩGround resistor R₁ (non-inverting gain)Units: kΩ, Ω, MΩ

### Example values

How the main result changes when **Resistance R** changes and everything else stays at the example values above:

Resistance R (R₁ for inverting) (kΩ)Cutoff frequency f_c (Hz)53,183.09897.52,122.0659101,591.549412.51,273.2395151,061.03320795.7747

## Worked example

Inputs — Filter type: Passive RC; Resistance R (R₁ for inverting): 10 kΩ; Capacitance C: 10 nF.

Results — **Cutoff frequency f_c = 1,591.54943 Hz**; Passband gain = 1 V/V; Passband gain in dB = 0 dB.

## Key terms

- **Anti-aliasing**: Filtering before sampling to avoid false frequencies.

## FAQ

**What is a low-pass filter used for?**
Smoothing, anti-aliasing and removing high-frequency noise.

**What is the phase shift at cutoff?**
−45° for a first-order filter.

**Why does the inverting filter use R₂ for f_c?**
The capacitor sits in parallel with the feedback resistor.

**How do I get steeper roll-off?**
Cascade stages or use higher-order designs (Sallen–Key, etc.).


## Sources

- [OpenStax – University Physics Volume 2](https://openstax.org/details/books/university-physics-volume-2)
- [The Engineering ToolBox](https://www.engineeringtoolbox.com/)