Sum Function (Reporting Services)
Returns the sum of all the non-null numeric values specified by the expression, evaluated in the given scope.
The set of data specified in the expression must have the same data type. To convert data that has multiple numeric data types to the same data type, use conversion functions like CInt, CDbl or CDec. For more information, see Type Conversion Functions.
The value of scope cannot be an expression and must refer to the current scope or a containing scope.
The following two code examples provides a sum of line item totals in the Order group or data region.
=Sum(Fields!LineTotal.Value, "Order") ' or =Sum(CDbl(Fields!LineTotal.Value), "Order")