Estimate the Size of a Table
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Azure Synapse Analytics
Analytics Platform System (PDW)
SQL database in Microsoft Fabric
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 Estimate the Size of a Heap or Estimate the Size of a Clustered Index.
For each nonclustered index, calculate the space required for it by following the instructions in Estimate the Size of a Nonclustered Index.
Add the values calculated in steps 1 and 2.
See Also
Estimate the Size of a Database
Estimate the Size of a Heap
Estimate the Size of a Clustered Index
Estimate the Size of a Nonclustered Index