I'm sure I clicked in 'calculating index key size' when I looked at BOL, but the info is actually in 'Estimating the size of a nonclustered index'. I am using the SQL 2008 May 2009 BOL.
BOL is saying there is extra overhead if any varying length fields appear in an index, plus overhead for every varying length column.
Variable_Key_Size = 2 + (Num_Variable_Key_Cols x 2) + Max_Var_Key_Size
Max_Var_Key_Size also has its own calculation
The overhead is not much, but more than the 'correct' answer to the question implied.
Original author: https://github.com/SQL-FineBuild/Common/wiki/ 1-click install and best practice configuration of SQL Server 2019, 2017 2016, 2014, 2012, 2008 R2, 2008 and 2005.
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