Excel formula to count letters only from a given cell

=SUMPRODUCT((MID(A1,ROW(INDIRECT("A1:A"&LEN(A1))),1)>="A")*(MID(A1,ROW(INDIRECT("A1:A"&LEN(A1))),1)<="Z"))

For Example

If A1 = "Wor12d".~!@#$%^&*()_+{}|":<>?

then this formula would return the result as 4 since there are only four letters in the cell.