What is the noun form of loudly?

There isn't a direct noun form of "loudly" in English. "Loudly" is an adverb, describing how something is done.

To express the noun form of "loudly," you would need to use a phrase like:

* Loudness

* Loud sound

* Volume

* Intensity

For example:

* "The music was playing loudly." (adverb)

* "The loudness of the music was unbearable." (noun)

* "The volume of the music was turned up too high." (noun)