📡 Resistor Noise Calculator
Estimate the thermal (Johnson-Nyquist) noise voltage and current generated by a resistor at a given temperature and bandwidth.
What is resistor thermal noise?
Every resistor generates a small random voltage fluctuation caused by the thermal motion of electrons inside it, even with no current flowing. This is called Johnson-Nyquist noise, and it sets a fundamental noise floor for electronic circuits, especially sensitive amplifiers and receivers.
The formula
The RMS noise voltage is given by Vn = √(4kTRB), where k is Boltzmann’s constant (1.380649×10-23 J/K), T is absolute temperature in kelvin, R is resistance in ohms, and B is the measurement bandwidth in hertz. The corresponding noise current is In = Vn / R.
Enter the resistance, temperature in Celsius, and bandwidth of interest to get the expected RMS noise voltage and current. This is a theoretical minimum — real circuits typically have additional noise sources on top of this thermal floor. For general engineering reference and education only.