The document is archived and information here might be outdated
Estimating the Size of a Table
You can use the following steps to estimate the amount of space required to store data in a table:
Calculate the space required for the heap or clustered index following the instructions in Estimating the Size of a Heap or Estimating the Size of a Clustered Index.
For each nonclustered index, calculate the space required for it by following the instructions in Estimating the Size of a Nonclustered Index.
Add the values calculated in steps 1 and 2.