How Azure Backup Vault compress SQL DB backups via MABS?

Hi There,

I will basically would like to know how Azure Backup Vault compress SQL DB backups taken by MABS in order to be able to calculate cost.

For example, I have a DB which size is 2.5 TB, will Azure Backup store the full DB size or it will be compressed? If compressed, what is the the compression percentage?

Thank you very much in advance to those providing any answer.

Regards,
Ricardo