OneNote stores cached notebooks, images, and attachments locally for offline access, which can grow to hundreds of megabytes on your phone. You can clear that storage on iPhone and Android without losing notes, because your notebooks are synced to OneDrive in the cloud.

Short answer:

  • Android: go to Settings > Apps > OneNote > Storage and tap Clear cache (safe). Clear storage signs you out.
  • iPhone: there's no in-app cache button, so offload OneNote via iPhone Storage or delete and reinstall it.
  • Your notebooks live in OneDrive, so they resync after a cache clear, confirm everything has synced first.

Why OneNote Builds Up Storage

OneNote caches the notebooks you've opened plus their images, PDFs, audio clips, and file attachments so you can read and edit offline. Image- and attachment-heavy notebooks make this cache grow fast.

On iPhone, check Settings > General > iPhone Storage > OneNote, where the cache shows under Documents & Data. On Android, open Settings > Apps > OneNote > Storage.

The reassuring part: this is mostly a synced copy. Your notebooks live in OneDrive under your Microsoft account, so the local cache is rebuildable. The one rule before clearing: make sure recent edits have synced.

Sync First, Then Clear (Important)

OneNote saves edits locally and syncs them to the cloud, so confirm syncing is complete before you clear anything, to avoid losing unsynced changes.

  1. Open OneNote and make sure you have a network connection.
  2. Open your Notebooks list; pull to refresh or tap the sync option in settings to force a sync.
  3. Wait until no "syncing" or "pending" indicators remain.

Once everything shows as synced, the local cache is fully reproducible from OneDrive and safe to clear. This step protects any note you edited offline or just before cleaning up.

Clear OneNote Cache on Android (Safest)

After syncing, Android gives you a clean cache clear that won't sign you out.

  1. Open Settings > Apps (or Apps & notifications).
  2. Tap OneNote, then Storage (or Storage & cache).
  3. Tap Clear cache.

Only temporary cached files are removed. OneNote redownloads notebooks from OneDrive as you open them, so the app keeps working and you stay logged in. Repeat whenever the cache builds back up.

Cache vs Clear Storage: Read Before Tapping

The second button on that Android screen is far more drastic, so be careful.

  • Clear cache: removes temporary files only. Safe, keeps you signed in.
  • Clear storage / Clear data: wipes everything local, signs you out, and discards any unsynced notes.

Always use Clear cache for cleanup. Only use Clear storage if you've confirmed every note has synced and you're ready to sign back in.

Clear OneNote Storage on iPhone

iOS has no per-app cache button, and OneNote doesn't include an in-app clear option, so you reset it from iOS after syncing.

Go to Settings > General > iPhone Storage > OneNote:

  • Tap Offload App to remove the app while keeping its data, then reinstall to clear cached files.
  • Tap Delete App for a full wipe, then reinstall from the App Store and sign back in.

Because your notebooks live in OneDrive, signing back in resyncs them. Just double-check that recent offline edits synced before a full delete, since unsynced changes only exist on the device.

Keep OneNote and Your Phone Lean

A simple habit keeps OneNote's footprint small:

  • Make sure notebooks sync, then clear the cache (Android) or offload (iPhone) every few weeks.
  • Keep large attachments and media in fewer, well-organized notebooks so less is cached at once.
  • Check your phone's storage screen occasionally to confirm OneNote stays in check.

OneNote is one app among many, and the rest of your phone usually needs attention too. A review-first cleaner, Clenoir on iOS or Cleanor on Android, scans on-device and surfaces your largest files and duplicate photos before you confirm any deletion. For a fuller plan, see the clean up phone storage hub and the storage cleanup FAQ. With notes synced and the cache cleared, OneNote keeps working exactly as before while every notebook stays safe in the cloud.

Want the fast version? Cleanor for iPhone scans on-device — nothing uploaded — and surfaces your largest videos, duplicate photos, and heavy caches in one pass. For the full routine, see the free up phone storage guide.

FAQ

Will clearing OneNote storage delete my notes?

No, because your notebooks live in OneDrive under your Microsoft account, so the local cache is rebuildable and resyncs after a clear. The one rule is to confirm recent edits have synced first, since unsynced offline changes only exist on the device.

How do I make sure OneNote has synced before clearing the cache?

Open OneNote with a network connection, open your Notebooks list, pull to refresh or use the sync option in settings to force a sync, and wait until no "syncing" or "pending" indicators remain. Once everything shows as synced, the cache is fully reproducible from OneDrive and safe to clear.

How do I clear the OneNote cache on Android?

After syncing, open Settings > Apps (or Apps & notifications), tap OneNote, then Storage (or Storage & cache), and tap Clear cache. Only temporary cached files are removed and OneNote redownloads notebooks from OneDrive as you open them, so you stay logged in.