# Resistor Noise Calculator (Johnson–Nyquist)

URL: https://speedycalculator.com/calculators/physics/resistor-noise/
Last updated: 2026-10-30

> The resistor noise calculator finds the thermal (Johnson–Nyquist) noise voltage of a resistor from its resistance, temperature and measurement bandwidth, in volts, dBu and dBV.

## Inputs

- Resistance R (kΩ, Ω, MΩ)
- Temperature (K, °C, °F)
- Bandwidth Δf (kHz, Hz, MHz)

## Results

- Noise voltage (RMS)
- Noise density
- Level in dBu
- Level in dBV

## Formula

```
V_n = √(4·k_B·T·R·Δf)
```

## Explanation

Every resistor hisses: its electrons jiggle with thermal energy, producing a small random voltage. It sets the ultimate noise floor of audio preamps, radio receivers and sensors – which is why low-noise designs use low resistances or cool their circuits.

### How to use the Resistor Noise Calculator

- **Resistance R**
- **Temperature**
- **Bandwidth Δf**

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

### How it works

Enter the resistance, the temperature and the bandwidth.

### Inputs explained

FieldWhat to enterResistance RUnits: kΩ, Ω, MΩTemperatureUnits: K, °C, °FBandwidth ΔfUnits: kHz, Hz, MHz

### What each result means

- **Noise voltage (RMS)** = sqrt(4×1.380649e-23×[Temperature]×[Resistance R]×[Bandwidth Δf])
- **Noise density** = sqrt(4×1.380649e-23×[Temperature]×[Resistance R])×1e9
- **Level in dBu** = 20×log10([Noise voltage (RMS)]÷0.7746)
- **Level in dBV** = 20×log10([Noise voltage (RMS)])

### Example values

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

Resistance R (kΩ)Noise voltage (RMS) (µV)51.28727.51.5764101.820312.52.0352152.2294202.5743

## Worked example

Inputs — Resistance R: 10 kΩ; Temperature: 300 K; Bandwidth Δf: 20 kHz.

Results — **Noise voltage (RMS) = 1.82032 µV**; Noise density = 12.87159 nV/√Hz; Level in dBu = -112.579 dBu; Level in dBV = -114.797 dBV.

## Key terms

- **Johnson–Nyquist noise**: Thermal noise from charge carriers in a resistor.

## FAQ

**What is the noise of a 1 kΩ resistor?**
About 4 nV/√Hz at room temperature.

**Can noise be avoided?**
Only by lowering resistance, temperature or bandwidth.

**Is all resistor noise thermal?**
No – excess (current) noise depends on construction; metal film is best.

**Why does bandwidth matter?**
Noise power is spread evenly across frequency.


## Sources

- [OpenStax – University Physics Volume 2](https://openstax.org/details/books/university-physics-volume-2)
- [HyperPhysics (Georgia State University)](http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html)
- [NIST – Fundamental physical constants](https://physics.nist.gov/cuu/Constants/)