Noise Figure Calculator

Calculate RF noise figure, linear noise factor, and equivalent noise temperature from input and output signal-to-noise ratios.

RF noise performance

Enter both signal-to-noise ratios in decibels. The input SNR must be at least as large as the output SNR.

Input Signal-to-Noise Ratio (dB)

Output Signal-to-Noise Ratio (dB)

About noise figure

Noise figure describes how much a real electronic device degrades the signal-to-noise ratio that passes through it. Every amplifier, mixer, filter, cable, and receiver stage adds some noise or loss, so the output signal-to-noise ratio is normally lower than the input ratio. Engineers use noise figure to compare RF and microwave components independently of their gain. A lower value means the component preserves weak signals more effectively, which is especially important in the first stage of a radio receiver. When both ratios are expressed in decibels, noise figure is simply input SNR minus output SNR. For example, a device receiving a 20 dB input SNR and delivering an 18 dB output SNR has a 2 dB noise figure. The related noise factor is a linear ratio rather than a decibel value. It equals ten raised to the noise figure divided by ten. An ideal noiseless component has a factor of one and a figure of zero decibels. Equivalent noise temperature expresses the same degradation as the temperature of a hypothetical matched noise source. Under the conventional reference temperature of 290 kelvin, equivalent temperature equals 290 multiplied by noise factor minus one. This representation is common in radio astronomy, satellite links, low-noise amplifier specifications, and antenna system calculations. It should not be confused with the device's physical temperature; it is an electrical noise model that makes system analysis convenient. Noise figure matters most near the receiver input. Friis analysis shows that the first stage's factor contributes directly, while later stages are divided by the preceding gain. A low-noise amplifier with adequate gain can therefore protect the system noise performance from noisier downstream circuitry. Loss before that amplifier, including cable and filter loss, directly worsens the receiver noise figure and can erase the benefit of a high-quality amplifier. This calculator assumes input and output SNR measurements use the same bandwidth, impedance convention, and signal definition. Mismatched measurement bandwidths produce a misleading result because integrated noise depends on bandwidth. Values should also represent power ratios converted consistently to decibels. Use the result for component comparison or as one input to a cascaded noise calculation; a complete link budget must additionally account for antenna temperature, path loss, gain, interference, required demodulation margin, and measurement uncertainty.

Noise figure examples

SNR measurements	Calculated result	Typical context
20 dB in, 18 dB out	NF 2 dB, factor 1.5849	A practical low-noise RF amplifier.
30 dB in, 27 dB out	NF 3 dB, factor 1.9953	The device nearly doubles input-referred noise power.
15 dB in, 14.5 dB out	NF 0.5 dB, factor 1.1220	Very low degradation in a receiver front end.
40 dB in, 34 dB out	NF 6 dB, factor 3.9811	A relatively noisy stage or passive loss.

How to calculate noise figure

Enter the input signal-to-noise ratio measured in decibels.
Enter the output signal-to-noise ratio measured over the same bandwidth.
Select Calculate noise figure.
Use the decibel figure, linear factor, or equivalent temperature required by your noise budget.

Noise figure calculator FAQ

What is a good noise figure?

The answer depends on frequency, technology, gain, and application. Receiver front ends often target the lowest practical value, while later stages can tolerate more noise.

Can noise figure be negative?

A passive or ordinary stable amplifier should not improve SNR, so its noise figure is nonnegative. Apparent negative values usually indicate inconsistent measurements, bandwidths, or calibration.

What is the difference between noise figure and noise factor?

Noise factor is the linear ratio of input SNR to output SNR. Noise figure expresses that same ratio in decibels, making cascades and specifications easier to compare.

Why is 290 K used for equivalent noise temperature?

A reference temperature of 290 kelvin is the established standard for noise-factor calculations. It is close to room temperature and provides a consistent comparison basis.

Does amplifier gain affect noise figure?

A component's own noise figure describes SNR degradation rather than gain alone. In a cascade, however, high first-stage gain reduces the impact of the noise factors of later stages.