The SUM function adds values. You can add individual values, cell references or ranges or a mix of all three. For example: =SUM (A2:A10) Adds the values in cells A2:10. =SUM (A2:A10, C2:C10) Adds the values in cells A2:10, as well as cells C2:C10. Syntax: Best Practices with SUM. Frequently Asked Questions. Need more help?