The standard formula (assuming no blanks in A1:A20) is:

=SUMPRODUCT(1/COUNTIF(A1:A20,A1:A20))

HTH
Jason
Atlanta, GA

"Kanwaljit Singh Dhunna" wrote:

A1:A20 contains 4 unique names. Formula applied in B1 should give the result
that how many No. of Unique names are there in range A1:A20 (i.e., the result
should be 4)