Storage Unit tool displays current storage usage in the organization. You can view available data and file storage usage. It displays data storage, file storage, top users by data and file storage. It also displays largest files in order of sizes.
Setup > Data Management > Storage Usage
Current Data Storage Usage: Displays storage usage of individual objects.
Current File Storage Usage: Displays storage usage of Documents and Photos which contain files.
Top Users by Data Storage Usage: Displays data storage usage of individual users
Top Users by File Storage Usage: Displays file storage used by individual users who have saved the documents in the salesforce.
Click Overall Top Files by Storage Utilization
Displays largest file in order.