Noise Figure Calculator

How to use this noise figure calculator

What this calculator does

This calculator estimates how much a device or cascade degrades signal-to-noise ratio. It supports the four common data paths represented in the controls: linear Signal-to-noise ratios, Signal-to-noise ratios in dB, direct Noise factor conversion, and Cascaded amplifiers. The primary result is Noise figure in decibels, while Noise factor shows the same degradation as a linear ratio. For cascades, it also reports Total gain and a stage-by-stage Friis breakdown. This is an engineering calculation, not a substitute for a calibrated measurement setup, impedance-match analysis, bandwidth definition, or uncertainty budget. Rohde & Schwarz's overview of noise figure measurements and SNR explains why the metric is central to RF receiver testing.

When to use it

Use this calculator when you want to compare an input and output SNR measurement, convert a published linear noise factor to dB, check whether an RF component's stated SNR degradation is plausible, or estimate the total noise figure of a receiver chain before hardware is assembled. The cascade mode is especially useful for exploring why a low-noise first stage with adequate gain can dominate overall receiver performance.

How to calculate

1. The calculator opens with a ready-to-use two-stage demonstration: stage 1 has a 1.2 dB noise figure and 18 dB gain; stage 2 has a 4 dB noise figure and 12 dB gain. The results and a validated XLSX export are available immediately.
2. Choose Find noise figure using... to match the form of your data. Replace the demonstration values with your own measurements or component specifications. Values use a dot as the decimal separator; commas are accepted only as standard thousands grouping.
3. Read Noise figure as the SNR loss in dB and Noise factor as the same degradation in linear form. In cascade mode, review Total gain and the detail table to see how later stages are reduced by preceding gain.
4. Select Download Excel to export the current validated model, including inputs, results, and stage detail. Reset clears the demonstration and all data values; after reset, Excel export remains disabled until you enter a complete valid input set again.

Input guide

Find noise figure using... is required and selects the formula path. In Signal-to-noise ratios mode, Input SNR and Output SNR are required positive linear power ratios between 10⁻¹² and 10¹²; for example, 8 and 7. Input SNR must be at least as large as output SNR for the passive-noise-degradation interpretation used here. A common mistake is entering dB values into these ratio fields. In Signal-to-noise ratios in dB mode, the two Input SNR and Output SNR fields accept values from – 300 to 300 dB; an example is 40 dB input and 35 dB output. Their difference is the noise figure. In Noise factor mode, Noise factor is a required unitless value from 1 to 10⁶⁰; 2 corresponds to about 3.0103 dB. Values below 1 are rejected because they would imply a negative noise figure under this model.

In Cascaded amplifiers mode, Number of amplifiers is required and may be 2 through 10. Every generated Noise figure – stage 1 through Noise figure – stage 10 field is required for the selected stage count and accepts 0 to 60 dB. Every corresponding Gain – stage 1 through Gain – stage 10 field is required and accepts – 60 to 60 dB. Gain may be negative to represent a lossy stage, although a chain with heavy early loss will usually have a much worse total noise figure. The cascade calculation converts each dB noise figure and gain to linear form before applying Friis' equation. Do not add stage noise figures directly; only gains in dB add directly across a cascade.

Output guide

Noise figure is the primary result in dB. Zero means no SNR degradation in the idealized definition; larger values mean more degradation. Noise factor is the equivalent linear ratio and is exactly related by NF = 10 log₁₀(F). A factor of 1 corresponds to 0 dB. Total gain appears only for cascades and is the sum of the stage gains in dB. The summary pills repeat the current Mode, Noise figure, Noise factor, and, for cascade mode, the number of Stages.

The Cascade detail table lists Stage, Noise figure (dB), Noise factor, Gain (dB), Linear gain, and Friis term. The Friis term is the contribution of that stage to total linear noise factor after division by preceding linear gain. For non-cascade modes, the table becomes a compact calculation detail table showing the entered quantities and the derived ratio or dB conversion. These are deterministic formula outputs, not recommendations or measured uncertainty bounds.

Worked example

With the startup cascade, stage 1 has NF₁ = 1.2 dB and G₁ = 18 dB, while stage 2 has NF₂ = 4 dB and G₂ = 12 dB. Converting to linear form gives F₁ = 1.3182567, F₂ = 2.5118864, and G₁ = 63.0957344. Friis' two-stage relation gives Ftotal = F₁ + (F₂ – 1)/G₁ = 1.3422185. Converting back to decibels gives Noise figure = 1.2782 dB. The gains add to Total gain = 30.0000 dB. These values match the first-open result cards, the cascade detail table, and the startup Excel workbook.

Learn more

For a deeper treatment of multi-stage receiver analysis, see Analog Devices' discussion of system noise-figure analysis for radio receivers. For practical instrument context, Keysight's noise figure measurement application notes describe measured noise figure as an RF test quantity alongside gain.