This article explains how ProBackup calculates your total data storage so you can manage your backup usage effectively.
​

Each unique record is counted once toward your data usage. On average, a single record takes up approximately 15 KB, including all associated revisions and encryption overhead.
​

Files and attachments typically account for 90–95% of your total storage. Their storage is calculated based on the original file size.
​

When records or files are deleted from your source app, they are still retained in your backup and continue to count toward your total storage. These items are permanently removed only after your configured retention period has passed.