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Resistor Thermal Noise Calculator — Johnson Noise Voltage & Density
Calculate Johnson-Nyquist RMS noise voltage and spectral density from resistance, absolute temperature and bandwidth.
Last updated: September 16, 2026
Results
Noise density 12.87159 nV/√Hz
RMS noise 1.820318 µV
Formula, example and assumptions
en=√(4kTR) V/√Hz; Vrms=√(4kTRB).
10 kΩ at 300 K is about 12.9 nV/√Hz before amplifier noise is added.
- White Johnson noise model over the entered bandwidth.
- 1/f noise, amplifier noise, filtering shape and parasitic effects are separate.
Frequently asked questions
Does a larger resistor make more voltage noise?
Yes; voltage-noise density rises with the square root of resistance.
Why does bandwidth matter?
Independent white-noise power accumulates across bandwidth, so RMS voltage scales with √B.