If your C drive is full and your disk has unallocated space, Windows 10 can add that space to C with Disk Management. There is one catch: Extend Volume only works when the unallocated space sits directly to the right of C in the disk map. Back up important files before changing partitions. Windows 10 reached end of support on October 14, 2025. Consumer Extended Security Updates (ESU) now run until October 12, 2027.
Quick Answer
Right-click Start, open Disk Management, right-click the C drive, choose Extend Volume, and follow the wizard to add the unallocated space. If Extend Volume is greyed out, the free space is not directly after C.
How to Extend the C Drive in Windows 10
- Back up important files.
- Right-click the Start button and choose Disk Management.
- Check that Unallocated space appears immediately to the right of the C: partition on the same disk.
- Right-click C: and choose Extend Volume, then click Next.
- Keep the suggested amount (or enter a smaller one), click Next, then Finish. C now includes the extra space.
Why Extend Volume May Be Greyed Out
| Situation | What it means |
|---|---|
| Recovery partition between C and free space | The space is not adjacent |
| Unallocated space on a different disk | Cannot extend across disks this way |
| No unallocated space | Shrink another partition first |
| Space is a free partition, not unallocated | Delete that partition only if it holds nothing you need |
Troubleshooting
- A recovery partition blocks the space: moving or removing it is advanced and risky. Consider a reputable partition tool, and always back up first.
- You do not have unallocated space: shrink another volume in Disk Management, or free up space instead.
- For simpler ways to reclaim room, see how to increase C drive space in Windows 10.
- To clean up files first, read how to free up disk space on Windows.
Frequently Asked Questions
Will extending C delete my files?
Extending into unallocated space does not delete files on C, but always back up before partition changes.
Can I undo it?
You can shrink the volume again, though Windows may not be able to shrink it by the full amount.
Does this work on Windows 11?
Yes. Disk Management works the same way.
Summary
- Back up first.
- Open Disk Management.
- Right-click C: and choose Extend Volume.
- Check that unallocated space is right after C.
Kermit Matthews is a freelance writer based in Philadelphia, Pennsylvania with more than a decade of experience writing technology guides. He has a Bachelor’s and Master’s degree in Computer Science and has spent much of his professional career in IT management.
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