You can sum a series of numbers in Microsoft Excel manually by typing in a simple formula, or automatically with a tool.

You can't use a SUM() function to sum a filtered list, unless you intend to evaluate hidden and unhidden values. Here's how to sum only the values that meet your filter's criteria.

You can sum cells across multiple sheets in Excel. This article presents steps for Adding single-cell values or Adding values in the range of cells.

SUM is the spreadsheet equivalent of an open invite: it welcomes everything into the total, whether it belongs there or not.