AOMEI Partition Assistant Standard is FREE disk partition software that allows you to completely control your hard disk and partitions. For example, the ” Resize Partition” enables you to extend partition size to solve low disk space problems, or shrink partition size etc. In this article, I will show you how to fix unable to Extend Volume on Windows protected by BitLocker.
You can flexibly manage disk space with “Create Partition”, “Merge Partitions”, “Delete Partition”, “Format Partition”, “Copy Partition” and so on. AOMEI Partition Assistant embeds sector-level data protection technology.
AOMEI Partition Assistant doesn’t support merging non-adjacent partitions. This is also why you are unable to Extend the C Drive. Do not create a new Partition out of the volume. Thereafter, then you can merge the host partition and the unallocated space together after performing Resize/Move Partition operation. See this link for more scenarios this Tool does not support.
Note: I could not Merge unallocated space into C Partition for whatever reason and this was why I used the method above.
Error “Unable to Extend Volume in Windows Protected by BitLocker”
It’s impossible to extend a partition protected with BitLocker. If this wasn’t the case, then you would have been able to follow these steps on how to Extend a VM Hard Disk on VMware Workstation. But oftentimes, the Extend Volume will be greyed even when BitLocker is disabled because of the reasons below.
To extend the BitLocker partition, disable BitLocker and the unallocated space must be adjacent before or behind the partition. I will be using the AOmei Partitioning tool to realise that the drives are adjacent.
You may run into issues where the Extend Volume on the C drive is greyed out. This error is not uncommon. Please see How to Extend System Drive Partition on Windows, and How to Extend Proxmox Local Container Storage. The following steps will help you extend the volume greyed out.
As you can see the Extend Volume is unusable. 
Fix unable to Extend Volume on Windows
Before proceeding with the steps below, Please see if you can extend the Volume as your scenario might be different from mine.Disable BitLocker
Before embarking on the steps below, Please Disable BitLocker on Windows to see if you can extend. Most times, this is possible. You can also use AOMEI to disable BitLocker. You will see these steps very shortly.
Download Aomei free partition manager
AOMEI Partition Assistant Standard is the right one for your PC, guaranteeing you get a full suite of features for creating, resizing, deleting, merging, and splitting partitions, and so on. Please download AOMEI disk Partition Assistant.
As you can see, the tool has been downloaded.
Double-click on the Installer in order to install the Tool.
Select your desired to use for installation.
Close the AOMEI Assitsant Pro Edition.
Click on Install Now to install the AOMEI Partition Assistant.
As you can see the tool is been installed.
You have successfully installed the Aomei Partition Manager on your PC. You can close the Windows or click on ENjoy Now 🙂
When you click on Enjoy Now, you will be redirected to a page describing its features.
AOMEI Partition Assistant Standard Edition
To extend the BitLocker partition, there must have unallocated space adjacently before or behind the BitLocker encrypted partition. Of course, you can also use the “Resize/Move Partition” function to realize it.
Right-click on the Unallocated drive, and select Resize/Move Partition.
Select the drive and click on Resize/move Partition. Do not forget to Apply the setting. If BitLocker is detected, you will be prompted to Turn Of BitLocker.
On the confirmation window, click on Yes.
As you can see, the Move and Resize Partition was completed successfully.
Please see BitLocker System Partition: Detailed steps to troubleshoot and fix System Partition not available or large enough [Part 2], How to get the Windows 10 Version 22H2 Update, and how to fix fatal Git error refusing to merge unrelated histories.
Merge Partition
Now that the drives are adjacent and can now be merged.
Note: If you wish to use AOMEI Partition Assistant for this, create a new partition of the unallocated space before merging. Else, it will not work.
As you can see from the Disk Management window, the partition is now adjacent to each other. As you can see, we have disabled BitLocker as well.
How to extend Volume on Windows via Disk Management
Please follow the steps highlighted in this article to extend Partition on Windows. Follow up from the Extend Partition section.
The drive is now extended successfully.
Enable BitLocker
Because I wish to have this drive protected, I will have to re-enable BitLocker on it. Please see this article to re-enable BitLocker. Please see how to Enable or Disable BitLocker Drive Encryption on Windows, and how to Force BitLocker Recovery mode: How to unlock BitLocker Protected Drive via MBAM.
Right-click on the Disk and select Turn on BitLocker. Follow through the steps.
I hope you found this blog post helpful on how to fix unable to Extend Volume on Windows protected by BitLocker. If you have any questions, please let me know in the comment section.