Ich kenne nur no. für number.

zotti, "no" wird eher für die Nummerierung benutzt, aber nicht für eine Anzahl.

"No." (with or w/o period) is used for concrete/specific numbers. For example, as in
N0. 10, Downing Street.
Sometimes (very seldom), one sees "Nbr." for an undetermined number. However, I find it strange. If I were to write it (and did not want to write out "number"), I would write
# of measurements

But isn't it ok to write "Nr." in a table of measurements or so?

e.g.

Colour Treatment Nr. of measurements
blue acetylation 10

The abbreviation for number is "no." in English not "nr."
number/no. = Zahl

number of/no. of = Anzahl
alternative for "number of" is also "quantity".
Abbreviation often used "qty" = Anzahl/Menge/Stückzahl