SUM

Adds a set of numbers.

Syntax

SUM(Number 1 [; Number 2 [; … [; Number 255]]])

Number 1, Number 2, … , Number 255 are numbers, references to cells or to cell ranges of numbers.

This function ignores any text or empty cell within a data range. If you suspect wrong results from this function, look for text in the data ranges. To highlight text contents in a data range, use the value highlighting feature.

Examples

=SUM(2;3;4) returns 9.

=SUM(A1;A3;B5) calculates the sum of the three cells.

=SUM(A1:E10) calculates the sum of all cells in the A1 to E10 cell range.

A formula such as =SUM((A1:A40>=C1)*(A1:A40<C2)*B1:B40) may be entered as an array formula by pressing the Shift+Enter keys instead of simply pressing the Enter key to finish entering the formula. The formula will then be shown in the Formula bar enclosed in braces and operates by multiplying corresponding elements of the arrays together and returning their sum.

SUM wiki page.

SUMIF, SUMIFS