To estimate your database size, you may use 100:1 ratio as an initial baseline for filesystem to database(DB) storage estimation (e.g. In 100GB of storage, you may use 1GB for database, which makes the database storage negligible for the most cases).
However, it is important to understand that there is no real "formula" or rule of a thumb here, since the ratio depends on many aspects, such as:
the size of artifacts, distribution of equal checksums, the type of database, whether or not archive indexing is enabled, the number of builds stored in Artifactory and the usage of metadata properties.
Therefore, our recommendation is to monitor the storage and re-evaluate it over time.