Noise Figure Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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Electrical results can look precise while a unit, operating mode, or component assumption quietly changes the answer. Noise Figure Calculator keeps the calculation tied to the quantities on this page, so you can trace the displayed cascaded noise figure back to the values you entered rather than treating it as a black-box number.

What this calculator does

The Noise Figure Calculator turns Find noise figure using…, Noise (stg. 1), Gain (stage 1), Noise (stg. 2) into the page’s Cascaded noise figure using the circuit or component relationship below. Where the page shows supporting quantities, they come from the same idealized model so you can cross-check the headline rather than reading one isolated number.

How to use it

Start with the fields that actually drive this result: Find noise figure using…, Noise (stg. 1), Gain (stage 1), Noise (stg. 2). Keep units consistent with the menus beside the fields and avoid mixing values measured under different conditions. Choose cascade or SNR method first because the required inputs and interpretation change with that selection. After calculating, change one input at a time if you are comparing scenarios; that makes cause-and-effect much easier to see.

How the calculation works

With the SNR method, noise figure in dB is NF = SNRin − SNRout. In the current two-stage cascade path, linear noise factor follows F = F1 + (F2−1)/G1 before conversion back to dB.

Example

Using the page’s default example (Find noise figure using… = cascade; Noise (stg. 1) = 1.5 dB; Gain (stage 1) = 10 dB; Noise (stg. 2) = 2 dB), the calculator reports Cascaded noise figure of 1.676206 dB. Change one driving input at a time and confirm the result moves in the direction predicted by the equation; that is a quick way to catch a unit or mode mistake.

How to interpret the result

Interpret the Cascaded noise figure as an idealized circuit/component quantity for the exact mode and units entered. Use it to compare designs or check hand calculations, but keep component tolerances, ratings, frequency dependence, and real operating conditions in view before turning the number into a hardware decision.

Limitations and notes

The current cascade calculation is a two-stage Friis-style path; the visible stage-count and second-stage gain fields do not expand it into an arbitrary N-stage cascade. Use a full cascade model when later-stage contributions matter.