Windows sometimes doesn't display extended partitions properly for reasons that I don't understand. 3rd party software seems to be more reliable. GParted shows the situation clearly on your screenshot: You have, in this order: 501 MB of unallocated disk space; 99.46 GB primary partition (NTFS, Windows root) 30 GB of unallocated space If you are using a USB 3.0 flash drive to install Windows 10, then this may also cause cannot create a new partition unallocated space issue in Windows 10. So, try the installation again using a USB 2.0 flash drive. Also Read: Fix Unknown USB Device in Windows 10. Method 3: Create Partition Using Diskpart In this case, Windows cannot extend the volume to the unallocated space. It means the "Extend Volume" function only works when the unallocated space is in the adjacent right side of the to-be-extended volume. While it's possible to extend the system partition using Windows Disk Management tool, there must be some unallocated space right next to the system partition. If you don't have some unallocated space next to the system drive, Windows will not show extend volume option even if you have enough free space on another partition. Step 3. Right-click on C: system partition and choose to Extend Volume on the dropdown options. Step 4. Follow the Extend Volume Wizard instructions and select default options to merge the two partitions for Windows 10 successfully. Step 5. Unallocated space on your hard drive is taking up valuable space but until it is allocated, Windows can't use it. Note that when you buy a hard drive, you cannot use the full amount .

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