Physics

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Resistor Noise Calculator.

Calculate Johnson-Nyquist RMS noise voltage and dBu/dBV levels from resistance, temperature, and bandwidth.

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Set your values

Results update as you type.

RMS noise voltage: 0.000001 V

RMS noise voltage

0.000000V
Noise level (dBu): -122.678881 dBu

Noise level (dBu)

0.000000dBu
Noise level (dBV): -124.897368 dBV

Noise level (dBV)

0.000000dBV

Results update automatically as you type.

Educational model. Inputs and assumptions are explicit; verify engineering or scientific decisions independently.

Use Cases

Audio circuit design

Estimate the thermal noise floor of resistors in audio preamps and mixers to ensure low noise performance.

Example: Check the noise of a 10 kΩ resistor at 300 K over a 20 kHz bandwidth.

Sensor signal conditioning

Determine the minimum detectable signal in sensor amplifiers by calculating the noise contribution of the input resistor.

Example: Evaluate a 1 MΩ resistor at 298 K with a 1 kHz bandwidth.

Frequently Asked Questions

What is Johnson-Nyquist noise?
Johnson-Nyquist noise, also known as thermal noise, is the random voltage generated by the thermal agitation of charge carriers in a conductor. It depends on resistance, temperature, and bandwidth, and is independent of frequency.
How do I use this calculator?
Enter the resistance in ohms, temperature in kelvin (or Celsius), and bandwidth in hertz. The calculator will compute the RMS noise voltage and its equivalent in dBu and dBV.
What are dBu and dBV?
dBu is a voltage level referenced to 0.775 V RMS, while dBV is referenced to 1 V RMS. These units are commonly used in audio engineering to express signal levels.

Tips & Common Mistakes

Tips

  • Use kelvin for temperature: 0°C = 273.15 K. Add 273.15 to Celsius values.
  • Bandwidth is the effective noise bandwidth of your system, not necessarily the -3 dB bandwidth.
  • For multiple resistors, calculate each noise voltage and sum them in quadrature (square root of sum of squares).
  • Lower resistance and temperature reduce thermal noise, but bandwidth is often fixed by the application.

Common Mistakes to Avoid

  • Forgetting to convert Celsius to kelvin, leading to incorrect noise voltage.
  • Using the full bandwidth of the signal instead of the noise-equivalent bandwidth.
  • Confusing dBu and dBV reference levels: dBu uses 0.775 V, dBV uses 1 V.

Last updated: August 13, 2026