Free up OneNote storage

OneNote notebooks live in OneDrive. This phone stores downloaded sections, ink, and file printouts. Clearing cache does not delete OneDrive notebooks. Deleting a page or emptying the Recycle bin does. Images, PDFs, and recordings on a page are the note, not leftover cache.

See how much space OneNote is using

iPhone

Open the iPhone Settings app.
Tap General > iPhone Storage.
Tap OneNote.

Android

Open your phone Settings > Apps.
Tap OneNote.
Tap Storage or Storage and cache.

Close notebooks you do not need on this phone

Open OneNote and open the notebooks list.
Close a notebook you can open from OneDrive later (Close / remove from this device, not Delete).

Closing drops the local copy. The notebook stays in OneDrive. Deleting a notebook is account data.

Sync before you clear anything

Pull to sync, or use settings > sync, until every notebook is up to date. Unsynced ink and photos exist only on this phone until that finishes.

Attachments and ink

File printouts, pictures, and audio on a page are the page content. Remove them only if you mean to change the notebook. That syncs as a real edit, not a cache clear.

Recycle bin

Deleted pages go to the notebook Recycle bin. Emptying it permanently removes them from OneDrive after the retention window.

Clear OneNote cache on Android

Open your phone Settings > Apps > OneNote.
Tap Storage or Storage and cache.
Tap Clear cache.

Do not tap Clear storage / Clear data unless you mean to sign out. Unsynced pages can be lost.

Reinstall the app if storage is still high

If you already cleaned media and OneNote still looks huge, a fresh install can clear leftover cache and temp files that are hard to reach by hand.

Wait until every notebook has finished syncing to OneDrive. Unsynced ink, photos, and file printouts live only on this phone until then.
Delete the app from your phone.
Restart your phone.
Install OneNote again from the App Store or Google Play.
Sign in and restore from backup if the app offers it.

This often frees a lot of space. You may need to download some media again after restore.

What to do next

After OneNote is lighter, check your photo library for duplicates and similar shots. That is what Dedupo is for.

More app guides: Free up app storage.