Estimating the Size of Dimension and Fact Tables

In most cases, when we started designing a data warehouse, as a data warehouse architect the PM needs us to tell them what the size of the DW will be, so that infrastructure can start the procurement process, capacity planning, etc. The problem is, we do not know the size of the warehouse until we finished building the warehouse and ETL. Below I describe the technique that I used to estimate the size of dimension and fact tables. Once you get that, you can estimate the size of the staging database based on the warehouse size (say 30-50% of DW size), size of the cubes (say 5-10% of DW size), size of the extract files (say 10-20% of DW size).