Thermal and shot noise calculator
A 50 Ω resistor at 290 K over 1 MHz produces about 0.9 µV rms of thermal noise. Calculate Johnson-Nyquist and shot noise, noise figure and temperature, SNR and ideal ADC limits.
Thermal noise voltage (rms) = 8.949e-7 V; Signal-to-noise ratio = 10.98 dB
| Thermal noise voltage (rms) | 8.949e-7 V |
|---|---|
| Thermal noise voltage density | 0.8949 nV/Hz^0.5 |
| Thermal noise current (rms) | 1.790e-8 A |
| Available noise power kTB | 4.004e-15 W |
| Available noise power kTB in dBm | -114 dBm |
| Noise power density kT | -174 dBm/Hz |
| Shot noise current (rms) | 1.790e-8 A |
| Shot noise current density | 17.9 pA/Hz^0.5 |
| Noise factor F | 1.995 |
| Noise temperature Te | 288.6 K |
| Input noise floor (290 K reference) | -111 dBm |
| Signal-to-noise ratio | 10.98 dB |
| Ideal ADC quantization SNR | 74 dB |
| Effective number of bits (ENOB) | 12 bit |
A 50 Ω resistor at 290 K over 1 MHz produces about 0.9 µV rms of thermal noise (Johnson-Nyquist). Enter resistance, temperature, bandwidth and DC current to get thermal and shot noise, then noise figure, SNR and the ideal ADC limit.
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Example: How much thermal noise does a 50 ohm resistor produce at 290 K over 1 MHz?
vn = sqrt(4 kB T R B); in = sqrt(4 kB T B / R); P = kB T B; in,shot = sqrt(2 q I B); F = 10^(NF/10), Te = 290 K (F – 1); noise floor = kB 290 K B F; SNR = P_signal / floor; SNR_ADC = 6.02 N + 1.76 dB; ENOB = (SINAD – 1.76) / 6.02.
Johnson noise of common cases at 290 K
| Resistance (Ω) | Bandwidth (Hz) | Voltage rms (µV) | Current rms (pA) | Power kTB (dBm) |
|---|---|---|---|---|
| 50 | 1,000,000 | 0.8949 | 17,900 | -113.98 |
| 50 | 20,000,000 | 4.002 | 80,040 | -100.96 |
| 1,000 | 1 | 0.004002 | 4.002 | -173.98 |
| 1,000 | 20,000 | 0.566 | 566 | -130.96 |
| 10,000 | 1,000,000 | 12.66 | 1,266 | -113.98 |
| 1,000,000 | 1,000 | 4.002 | 4.002 | -143.98 |
Cite this
ScienceShot. Thermal and shot noise calculator. https://scienceshot.com/noise-calculator.
More formats
ScienceShot. (2026). Thermal and shot noise calculator [Online calculator]. https://scienceshot.com/noise-calculator
@misc{scienceshot-noise-calculator-2026,
author = {{ScienceShot}},
title = {{Thermal and shot noise calculator}},
year = {2026},
note = {Online calculator},
url = {https://scienceshot.com/noise-calculator}
}Sources: J. B. Johnson, Thermal Agitation of Electricity in Conductors, Physical Review 32, 97 (1928); H. Nyquist, Thermal Agitation of Electric Charge in Conductors, Physical Review 32, 110 (1928); W. Schottky, Ueber spontane Stromschwankungen in verschiedenen Elektrizitaetsleitern, Annalen der Physik 362, 541 (1918); H. T. Friis, Noise Figures of Radio Receivers, Proceedings of the IRE 32, 419 (1944): 290 K reference temperature; W. Kester, Taking the Mystery out of the Infamous Formula SNR = 6.02N + 1.76 dB, Analog Devices MT-001 (2009); CODATA 2018 recommended values (Tiesinga et al., 2021), NIST: k and e.
Reviewed by a physicist with CERN experience