Windows 10 Extend Volume Greyed Out: Adding Free Space to Your C: Drive in Disk Management

Your C: drive is almost full, and Disk Management clearly shows unallocated space on the same disk. But when you right-click C:, “Extend Volume” is grey and cannot be selected. When Windows 10 Extend Volume greyed out blocks the obvious solution, the problem is almost always where the free space sits on the disk.

Disk Management can only extend a partition into unallocated space that sits directly to its right, with nothing in between. On many PCs, a recovery partition sits right after C:, so even a large block of free space further along the disk cannot be used.

Other limits apply too. MBR disks cannot have partitions larger than 2 TB, and a partition formatted with FAT32 cannot be extended at all.

Once you know which limit applies, there is usually a safe slot way around it.

What Usually Triggers It

The option is greyed out for these reasons:

• The unallocated space is not directly to the right of C:.
• A recovery partition sits between C: and the free space.
• The partition uses FAT32 or exFAT instead of NTFS.
• The space is on a different physical disk.

Free space shown in green as “Free space” belongs to an extended partition, which also cannot be added to a primary partition.

First Steps to Try

Look at the disk layout.

1. Right-click Start and select Disk Management.
2. Look at the bar for the disk that holds C:.
3. Check what is immediately to the right of C:.
4. If the unallocated space is directly next to C:, make sure C: is NTFS and try again.
5. If another partition, such as Recovery, is in the way, read the next steps.

If the Problem Continues

Deal with the partition in the way.

1. If the blocking partition is an old data partition you no longer need, copy its files elsewhere and delete it in Disk Management.
2. For a recovery partition, open Command Prompt as administrator and type reagentc /info to check whether it is in use.
3. Advanced users can disable recovery with reagentc /disable, delete the partition with diskpart, extend C:, then recreate recovery and run reagentc /enable.
4. Alternatively, use a well-known partition tool to move the recovery partition to the end of the disk.
5. After extending, check Settings > System > Storage to confirm the new size.

Protect Your Data First

Back up everything before deleting or moving partitions. A mistake in diskpart can erase the wrong partition instantly, and there is no undo button.

The Bottom Line

Extend Volume only works with unallocated space directly after the partition. Remove or move what sits in between, keep the partition NTFS, and always back up before changing the layout.