# Cutoff Frequency Calculator

URL: https://speedycalculator.com/calculators/physics/cutoff-frequency/
Last updated: 2026-10-30

> The cutoff frequency calculator finds the −3 dB cutoff frequency of a first-order RC or RL filter, and the time constant.

## Inputs

- Circuit
- Resistance R (kΩ, Ω, MΩ)
- Capacitance C (nF, µF, pF, F)
- Inductance L (mH, µH, nH, H)

## Results

- Cutoff frequency f_c
- Time constant τ
- Angular cutoff ω_c

## Formula

```
RC: f_c = 1/(2πRC),  τ = RC · RL: f_c = R/(2πL),  τ = L/R
```

## Explanation

At the cutoff frequency, a first-order filter passes half the power (−3 dB, or 70.7% of the voltage). Below it a low-pass filter passes signals; above it a high-pass filter does. Audio crossovers, anti-aliasing filters and tone controls are built this way.

### How to use the Cutoff Frequency Calculator

- **Circuit**
- **Resistance R**
- **Capacitance C**
- **Inductance L**

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

### How it works

Choose RC or RL and enter the component values.

### Inputs explained

FieldWhat to enterCircuitChoose one: RC, RLResistance RUnits: kΩ, Ω, MΩCapacitance CUnits: nF, µF, pF, FInductance LUnits: mH, µH, nH, H

### Example values

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

Resistance R (kΩ)Cutoff frequency f_c (Hz)5318.30997.5212.206610159.154912.5127.32415106.10332079.5775

## Worked example

Inputs — Circuit: RC; Resistance R: 10 kΩ; Capacitance C: 100 nF.

Results — **Cutoff frequency f_c = 159.15494 Hz**; Time constant τ = 1 ms; Angular cutoff ω_c = 1,000 rad/s.

## Key terms

- **Cutoff frequency**: Frequency at which output falls by 3 dB.

## FAQ

**What does −3 dB mean?**
Half the power, or 70.7% of the amplitude.

**Is it the same for low- and high-pass?**
Yes – the same formula, different arrangement.

**How steep is a first-order filter?**
20 dB per decade (6 dB per octave).

**How do I get a sharper filter?**
Use higher-order filters (more poles).


## Sources

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