Download “Limiter (2)” from here: Missing features - Audacity Support
That one does not exist yet. However, you can select a section of “noise only” and use “Wave Stats”.
Download “stats.ny” from here: "Wave Stats" plug-in
Instructions for installing the plug-ins: Missing features - Audacity Support
Note that the current “Wave Stats” plug-in is limited to analyzing a maximum duration of 30 seconds. There will be a new version (when I have time to complete and upload it) without this limitation.