Sheets' COUNT functions can help you count cells with numbers, text, or blank cells. Sheets actually has a small family of COUNT functions, but the most useful are:
COUNT: Counts cells that contain numbers; blank cells and cells with text aren't counted.
Syntax: = COUNT(D2:D55)
COUNTA: Counts cells that contain any kind of data, including numbers and text.
Syntax: = COUNTA(D2:D55)
COUNTBLANK: Counts blank or empty cells.
Syntax: = COUNTBLANK(D2:D55)
COUNTUNIQUE: Counts cells with unique values.
Syntax: = COUNTUNIQUE(D2:D55)
COUNTIF: Counts cells that meet a single criteria.
Syntax: = COUNTIF(D2:D55, "PARIS")