When your company purchased a Salesforce org., it will be allocated with a certain space of data storage, plus the number of licenses acquired and type of Salesforce edition. For the details, check the references below.
You can see the Used Data Space from Company Information in the setup menu. The screenshot below shows that Org has used 56% or 11.2MB of the allocated data storage.
To get the details of which object used the storage, navigate to Storage Usage under the setup menu.
Few things to note:
- Attachments will use file storage, not data storage. But Email Messages will use data storage.
- Most records are roughly 2 KB with some exceptions, see this article,
- such as Person Account (4KB for an Account and a Contact)
- EmailMessage records count as the actual size of the Email stored in HtmlBody and TextBody fields, e.g. a 100-KB email message used 100 KB of data storage space
- Rich text fields in an object still count as 2KB for each record
- Archived activities are not removed from Salesforce, and they still count for the storage usage
Reference:
- Data and File Storage Allocations
- Monitor Data and Storage Resources
- Salesforce record size overview
- Work with Archived Activities