PostgreSQL DB size estimation

Question

We are doing POC for DB selection. Based on our use case we got three recommendation

1. Postgres
2. Cassandra
3. Azure SQL

We are not going with Cassandra since we are not matching minimum requirements and we have two options left.

Before selecting db, how we can calculate how much size on disk is required for cost estimation.

(We have data volume, schema ready and yearly growth ready)

Answer 1

For Azure SQL Database, see Estimate the Size of a Database in the documentation.

Caveat: The instructions will allow only you to estimate the size of objects in uncompressed row store format.

Compression and column store format are much more difficult to estimate in advance, since so much depends on the data itself. See Data compression in the documentation, and related pages. You would likely need to create a physical database with a representative sample of the real data to arrive at a reasonable ballpark estimate.

For Postgres, see Proper storage size estimation technique for PostgreSQL