The limits that most often cause sync errors, at a glance. Detail and workarounds follow below.
| Limit | Value | What breaks when exceeded |
|---|---|---|
| Synced items (all libraries combined) | ~300,000 recommended maximum | Sync client slows, high CPU, delayed updates |
| Maximum file size (upload / download) | 250 GB per file or zip | Upload rejected |
| Total decoded path length | 400 characters (path + file name) | File fails to sync or upload |
| Single name segment (Windows) | 255 characters per folder or file name | Operating-system-level failure |
| Invalid characters in names | " * : < > ? / \ | |
File or folder will not sync |
Item count: the 300,000 threshold
The single most common cause of a sluggish OneDrive sync client is item volume. Microsoft recommends keeping the total number of synced items under roughly 300,000 across every library a user syncs. The count is cumulative: a user syncing five libraries of 70,000 items each is over the threshold even though no single library is large.
The symptom is not an error dialog. It is degradation: the sync client consumes more memory and CPU, status updates lag, and changes take longer to propagate. Because there is no hard stop, a tenant can drift past the limit gradually as libraries grow, then present as a vague "OneDrive is slow" helpdesk trend.
File size and path length
A single file can be up to 250 GB for upload and download through OneDrive and SharePoint in Microsoft 365. Very few document workloads approach this, but media, CAD, and backup archives can, so it is worth knowing where the ceiling sits.
Path length trips people up far more often. The total decoded file path, including the file name, must stay within 400 characters. Deeply nested folder structures with long, descriptive names run out of budget quickly. On Windows there is a second constraint: each individual segment (one folder or file name) cannot exceed 255 characters.
The decoded path is measured after URL-decoding, so a space counts as one character rather than the three characters of its encoded form.
Restricted characters and names
Certain characters cannot appear in file or folder names that sync. The set is:
- Characters:
"*:<>?/\| - A name cannot start or end with a space, and cannot end with a period.
- Certain reserved names (such as legacy device names) are blocked as whole file or folder names.
Files migrated from an on-premises file share are the usual source of illegal names, because Windows file servers historically allowed characters that SharePoint does not. A pre-migration scan that flags offending names saves a batch of failed items later.
Why these limits matter before a migration
Every one of these limits is really a migration concern in disguise. Content that lived happily on a file server for a decade can hit the 400-character path limit or carry an illegal character the moment it lands in SharePoint. Knowing the numbers up front lets you clean names and flatten folder depth before the move rather than triaging sync errors after it.
For the broader service ceilings that sit alongside these sync limits, see the SharePoint Online limits reference and the list view threshold reference. When you are ready to move content that respects these limits, Clone Master handles library and site migrations into SharePoint Online with full metadata fidelity.
Frequently Asked Questions
How many files can the OneDrive sync client handle reliably?
Keep the total under roughly 300,000 synced items across all libraries a user syncs. Beyond that combined count, the client slows regardless of how many items the user actively works with.
What is the maximum file path length in SharePoint Online?
The total decoded path, including the file name, cannot exceed 400 characters. On Windows, each individual folder or file name segment is also limited to 255 characters.
What is the largest file I can upload to SharePoint Online?
250 GB per file or zip for upload and download through OneDrive and SharePoint in Microsoft 365.
These values reflect Microsoft's documented defaults for OneDrive and SharePoint in Microsoft 365 and can change; confirm against current Microsoft documentation for a specific tenant configuration.
Last updated