Use these formulas for clustered and nonclustered indexes on dataonlylength tables.
Index rows containing variablelength columns require more overhead than index rows containing only fixedlength values.
Use this formula if the index contains only fixedlength keys defined as NOT NULL:
9 
(Overhead) 

+ 
Sum of fixedlength keys 

Size of index row 
Use this formula if the index contains any variablelength keys or columns that allow null values:
Formula 
Example 


9 
(Overhead) 
9 

+ 
Sum of length of fixedlength keys 
+ 
4 

+ 
Sum of length of variablelength keys 
+ 
20 

+ 
Number of variablelength keys * 2 
+ 
2 

Size of index row 
35 