How to Extend the C Drive in Windows 10

To extend the C drive in Windows 10, right-click Start and select Disk Management. Right-click the C: partition and select Extend Volume. Follow the wizard to add the unallocated space, then select Finish. This only works when the unallocated space sits right after C: on the same disk.

Applies to: Windows 10. Checked against Microsoft Learn on September 26, 2026.

Back up important files before changing partitions. See how to back up Windows 10.

Extend a partition with Disk Management

1. Right-click Start and select Disk Management.
2. Check that Unallocated space appears directly to the right of the partition you want to grow.
3. Right-click the partition, such as C:, and select Extend Volume.

4. Select Next.
5. Enter how much space to add, in MB. The maximum is filled in for you.
6. Select Next, then Finish.

The drive grows right away. You don’t need to restart.

If Extend Volume is greyed out

Disk Management can only extend into unallocated space that’s directly after the partition. Common causes:

• There’s no unallocated space. Shrink another partition on the same disk to make some, or free up space instead.
• Another partition is in the way. On many PCs a small recovery partition sits right after C:. Disk Management can’t move it, so the space after it can’t be added to C:.
• The space is on another disk. A partition can’t be extended onto a different drive.
• The partition isn’t NTFS. Only NTFS (and ReFS) volumes can be extended.

If the partition in the way holds only data you’ve backed up, you can delete it to make its space unallocated. See how to merge partitions in Windows 10.

If the recovery partition is in the way

This is an advanced fix. Back up your files and make a recovery USB drive first. It moves Windows’ recovery tools onto C:, removes the small recovery partition, and then extends C:. Open Command Prompt as an administrator:

1. Run reagentc /disable. This turns off the recovery environment and copies its files to C:.
2. Run reagentc /info and check that it says Disabled. Stop if you see an error.
3. Run diskpart, then list disk, select disk 0 and list partition. Find the Recovery partition right after C: and note its number.
4. Run select partition 4 using that number, then delete partition override, then exit.
5. Extend C: in Disk Management as shown above.
6. Run reagentc /enable and then reagentc /info to confirm the recovery environment is turned on again.

If reagentc /enable fails, Windows can still start normally, but use your recovery USB drive for repairs.

Extend with DiskPart

When unallocated space is right after C:, you can also run diskpart, then list volume, select volume C and extend. It uses all the unallocated space next to the volume.

Extend with PowerShell

PowerShell can do the same job in two commands. Open PowerShell as an administrator and run:

$max = (Get-PartitionSupportedSize -DriveLetter C).SizeMax
Resize-Partition -DriveLetter C -Size $max

The first line finds the largest size C: can grow to, and the second grows it to that size. The same rule applies: the unallocated space must be directly after C:. If the first number is the same as the current size, there’s nothing to add.

Extend C: in a virtual machine

If Windows 10 runs in a virtual machine and C: is full, make the virtual disk bigger first. Shut down the virtual machine, increase the disk size in Hyper-V Manager (Edit Disk > Expand), VirtualBox or VMware, then start Windows and extend C: with Disk Management as above. The new space appears as unallocated at the end of the disk. If a recovery partition sits after C:, see the section on that above.

Frequently asked questions

Can I shrink a partition to make space?

Yes. Right-click it in Disk Management and select Shrink Volume. The freed space appears after that partition, so it can only be added back to that same partition or used for a new one. See how to partition a hard drive in Windows 10.

Is there a way to free up space without changing partitions?

Yes. Try Disk Cleanup and deleting Windows.old.

Can I extend C: while Windows is running?

Yes. Extending works on the running system drive without a restart, as long as the free space is right next to it.

Will extending C: delete my files?

No. Extending only adds empty space to the partition. Deleting or shrinking other partitions is where data can be lost, so back up first.

Why does Shrink Volume offer less space than is free?

Some files, such as the page file or system restore data, sit near the end of the partition and can’t be moved. Disk Management stops at them. Turning off the page file or hibernation temporarily can free more.

Can third-party partition tools move the recovery partition?

Many can, and they’re easier than the commands above. Use a well-known tool from its developer’s own site and back up first.

To see how much space the C drive has left, see how to check disk space in Windows 10.

For other ways to open Disk Management, see how to open Disk Management in Windows 10.

Microsoft’s guide is Extend a basic or dynamic volume. More help is on our Windows Help & Guides page.