The free space is right there on the screen and Extend Volume is still grey. Windows is not broken — it is following one strict geometric rule it never explains. Here it is.
Few Windows moments are more frustrating than this: Disk Management shows gigabytes of unallocated space, you right-click the starving C drive, and Extend Volume sits grey and dead. This page explains the rule behind the refusal, the three causes that account for nearly every case, and — just as valuable — the list of popular fixes that cannot possibly work, so you can skip them.
Disk Management offers Extend Volume only when unallocated space lies immediately to the right of the partition, on the same disk, and the partition is formatted NTFS (or still unformatted). Miss any part of that sentence and the menu item greys out. It is not a bug, a permissions problem or an edition limit — Home, Pro and Server all behave the same way. Windows' built-in extend was designed to grow a partition into neighbouring empty space, never to rearrange a disk, and it refuses politely rather than moving your data around for you.
Because the refusal looks like a glitch, people try a familiar list of non-fixes: restarting, running Disk Management as a different user, disabling antivirus, shrinking D repeatedly, or converting the disk. None of them touch the geometry, so none of them can work. Shrinking D a second time only moves the free block further away. The only things that change the verdict are changing the layout itself — moving the blocking partition, removing and rebuilding it, or accepting the layout and freeing space inside C by other means. Those are the three real routes, and each has a case in this series.
Choose by what is blocking and what the data is worth. A recovery partition in the way is a small, well-understood obstacle — moving it with a partition tool, or rebuilding the recovery environment, are both reasonable, graded in their own case. A data partition full of files in the way argues for the mover tool, which shifts it intact, rather than a delete-and-restore afternoon. And if the blocked gain is only 10 or 15 GB, weigh it honestly against simply moving your biggest folders to D — sometimes the greyed-out button is doing you a favour. Whatever you choose, the backup case comes first: layout surgery without a backup is how a greyed-out button becomes a lost disk.
See the greyed-out problem diagnosed on a real disk, and the working route taken, in the full video.
▶️ Watch Full VideoNo. diskpart enforces exactly the same rule — the free space must be contiguous and immediately after the partition. Running extend in diskpart against a blocked layout simply returns an error saying there is not enough usable free space. The command line is a different door into the same room.
No, and converting a system disk purely for this would be a large risk taken for no benefit. The adjacency rule applies identically on GPT disks. What blocks you is the position of the free space, not the partition style.
Check the file system: Disk Management only extends NTFS (or unformatted) volumes, so a FAT32 C partition — rare, but seen on some dual-boot setups — will refuse. Also confirm the space really is on the same disk and is truly labelled Unallocated, not a partition with an empty file system.