Excel formula for SUM of Varying number of Rows in a Particular column

Hi Friends,
I have a similar requirement and am not able to find the solution. My requirement is i need excel formala to find the SUM of varying number of rows for a particular column.

For eg:
say my starting cell is A1.Data might populate from A1 to A3 in some instance and later from A1 to A10. So I need SUM of A1 to A3 or SUM of A1 to A10 in such cases. So please suggest me a formaula for this.

Any help on this would be greatly appreciated. Thanks

you can also name (let say r_data) a range (with Name Manager) with the following formula

=OFFSET(Sheet1!$A$1;0;0;COUNT(Sheet1!$A:$A);1)

and use the SUM(r_data). That range will expand and retract as you add or delete cells in column A.

just make sure your data are contigous