Thermal Noise Floor Calculator

Calculate thermal noise power (kTB) and system noise floor for any bandwidth and temperature.

What is the noise floor?

The noise floor is like background noise in a crowded restaurant — the minimum hum you can never fully eliminate. All electronic components generate random noise from heat, and your signal must be louder than this background noise to be heard.

Why does this matter?

Radio astronomers searching for faint signals from distant galaxies need incredibly low noise floors — even tiny amounts of heat in their receivers can drown out the signal. In everyday terms, a better noise floor means your receiver can detect weaker WiFi or GPS signals.

Parameters
Set bandwidth, temperature, and system noise figure.

The range of frequencies your receiver listens to. A wider bandwidth lets more signal through, but also lets in more noise. Pick a preset below or type your own.

The physical temperature of your receiver hardware. Hotter = more noise. 290 K is room temperature (≈ 17°C / 62°F). Cryogenic receivers run at just a few Kelvin to minimize noise.

How much extra noise your receiver hardware adds on top of the unavoidable thermal baseline. 0 dB = ideal noiseless receiver (not achievable in practice). Total cascaded noise figure of the receive chain.

Noise Floor
BW = 20 MHz, T = 290 K, NF = 3 dB
Noise Floor (dBm)-97.96 dBm
Noise Floor (dBW)-127.96 dBW
Noise Floor (watts)159.78 fW
Thermal noise only kTB (dBm)-100.96 dBm
Thermal noise kTB (watts)80.08 fW
Noise Spectral Density (kT)-173.98 dBm/Hz
NSD with NF-170.98 dBm/Hz
Equivalent Noise Temp.288.6 K
Bandwidth Context

1 Hz — Narrowband / CW

-171.0 dBm

1 kHz — SSB voice

-141.0 dBm

200 kHz — FM broadcast

-118.0 dBm

6 MHz — NTSC TV channel

-103.2 dBm

20 MHz — 802.11 WiFi

-98.0 dBm

The −174 dBm/Hz figure assumes T = 290 K per IEEE/ITU standard. Actual sky temperature for radio astronomy can be as low as 3 K (cosmic microwave background). Noise figure = 0 dB means ideal noiseless amplifier.