Salesforce Increasing Data Storage for customers with Spring ’19 Release
I came across this nugget with looking at the release notes for the upcoming Spring 19 release from Salesforce. The starting point for data storage in most Salesforce orgs is shifting from 1GB to 10GB. This is a big change and is especially good for smaller customers (initial allocated storage works off of the number of users).
The approximate rule of thumb is that a single record (e.g. an account, opportunity, case etc) will take up 2KB of data storage so 10Gb will mean starting point storage for approximately five million records. Thats a lot of records!
Enjoy Increased Data Storage
Data storage for select editions is increasing from 1 GB to 10 GB, giving you lots more room to grow. For example, previously a Professional Edition org with 10 users received 1 GB, because 10 users multiplied by 20 MB per user allotment is 200 MB. Now, a Professional Edition org with 10 users receives 10 GB + 200 MB.
Where: This change applies to Lightning Experience, Salesforce Classic, and all versions of the Salesforce app in Contact Manager, Group, Essentials, Professional, Enterprise, Performance, and Unlimited editions.
When: Orgs will begin to see the increase beginning in late March 2019.

More details on how data storage is allocated currently for salesforce customers: