Why is my OneDrive quota showing incorrect usage?

1. Check if the wrong items are being added to OneDrive – These can include large photos and videos, archived versions of documents, scanned copies of paper documents, and sent and received email attachments.
2. Check stored data – Files stored on an external hard drive, USB Key, or other storage devices that are connected to the device can be automatically added to OneDrive, even if they were added by accident.
3. Look into versions – If you have earlier versions of the file stored, it can take up extra storage space on OneDrive.
4. Delete unused or unnecessary files – You can delete them from both the device and OneDrive.