By Teresa / Last Updated February 25, 2020

Seagate 3TB hard drive not showing full capacity

“There is something wrong with my Seagate 3TB external hard drive which was bought a few days ago. The hard drive does not showing the full capacity in my Windows 7. I understand that there are different calculation methods for Windows operating system and hard drive manufactures. But the difference should not be that much. Simply put, my 3TB HDD only showing 2TB and I cannot make use of the left 952GB unallocated space. Is there any way to restore the HDD to full capacity?”

3TB HDD Shows 2TB only

Many a user find that their hard drive, especially external hard drive, USB hard drive, or portable hard drive does not showing full size when they use it. Usually, these types of hard drives are bigger than 2TB in size. In a few cases, 500GB or 1TB hard drive will not showing full capacity.

Apart from Seagate external hard drive, WD external hard drive, Hitachi hard drive, even Samsung hard drive does not escape such bad luck. It seems like missing space on the hard drive. Then, what are the possible causes for 3TB external HDD not showing full capacity?

Why does 3TB HDD not show full capacity?

When it comes to hard drive not showing full size, following reasons can account for the problem.

  • The 3TB hard drive has been initialized to a wrong partition table. If you find a formatted hard drive not showing full capacity, which is mainly because you format the 3TB hard drive to MBR partition table. As we all know, MBR partition table cannot address to the space that exceeds 2TB. As a result, to use a full capacity of a hard drive that is larger than 2TB, you need to initialize it to GPT partition table (see MBR vs GPT). That is the exact solution for the user in the example who uses Seagate external hard drive.

  • The 3TB external hard drive does not connect correctly. Some portable hard drive and USB hard drive are designed to connect a PC via a USB port. If you install the USB hard drive to your computer, the hard drive capacity detecting may become an issue. An accepted explanation is the controller board of USB hard drive breaks the 2TB limitation, yet Windows internal device controller does not. Therefore, you need to additional hardware to make the installed USB/portable hard drive showing full capacity. In that case, all you need to do is connecting the 3TB USB hard drive via USB port.

Other than those two main reasons, computer virus and hidden recovery partition are also possible causes for 3TB HDD not showing full capacity. Surely, they are also possible reasons for 4TB drive not showing full capacity. However, what count next is to find out how to solve this type of problems.

How to fix 3TB hard drive showing wrong capacity accordingly?

You need different solutions for the problem in different situations. Let’s get to know them one by one.

Convert 3TB HDD to GPT

If you initialized the 3TB to a wrong partition scheme when you first use it in Windows, don’t worry. Windows offers the option to change the partition scheme to the right one.

  • Method A. Convert to GPT disk in Disk Management

This method applies to new hard drive not showing full capacity issue. The option only works on an empty disk. If there is a partition on the disk, the Convert to GPT Disk will grayed out.

1. Click on Start, right click Computer (orThis PC) and select Manage. Click Disk Management in the left side.

2. Right click the 3TB HDD and select Convert to GPT Disk.

Convert to GPT Disk

  • Method B. Convert 3TB drive to GPT via Diskpart

This method applies to large capacity hard drive that has partitions formatted or files stored. It will first clean all data on the disk and then convert it to GPT. Therefore, backup important files if necessary.

1. Press Win + R to lift Run. Type diskpart and press OK. Run as administrator.

2. Input these commands in sequence and each command has an Enter followed by.

  • list disk

  • select disk n (where n is the disk number of the 3TB hard drive)

  • clean

  • convert gpt

  • exit

Convert GPT Diskpart

Go back to Disk Management and you should be able to use a full 3TB hard drive there.

  • Method C. Convert 3TB external to GPT without data loss

This method applies to 3TB external hard drive in any condition because it won’t delete existing partitions and files. In the first place, you need to download the free partition manager, AOMEI Partition Assistant Standard.

1. Install and run AOMEI Partition Assistant. Right click the 3TB HDD disk and selectConvert to GPT Disk.

Convert 3TB Disk to GPT

2. Confirm the operation by clicking OK.


3. Click Apply and then Proceed to commit the pending operation.

Apply 3TB

Tips: to convert system disk from MBR to GPT without data loss, please refer to AOMEI Partition Assistant Professional edition.

Wipe 3TB external HDD thoroughly

If the 3TB drive not showing full capacity problem does not result from wrong partition table, it could be the problem of computer virus or hidden recovery partition. As for hidden recovery partition, you can use the feature Change Drive Letter and Paths in Disk Management to make it visible.

As to the computer virus, it is suggested to clean the external drive. You can refer to steps in Method B to clean the 3TB disk in Diskpart, or you can wipe the 3TB disk completely and permanently with aforementioned free AOMEI Partition Assistant.

1. Open AOMEI Partition Assistant. Right click the 3TB hard drive and select Wipe Hard Drive.

Wipe Hard Drive 3TB

2. Choose Fill Sectors with Zero and click OK.

Fill Sectors with Zero 3TB

3. Also, click Apply and Proceed to execute the pending operation.

Apply 3TB

Tips: if you want to wipe all data on an SSD, upgrade toProfessional version and please refer to SSD data wiping with another feature, since HDD and SSD has different inner structure.

3TB hard drive only showing 746GB in Windows 7

When you get 3TB hard drive shows 746GB unallocated space in Disk Management, it could be the problem of incorrectly configured system settings, irregular entries in Registry, or Intel® Rapid Storage Technology (Intel RST).

You can easily fix the registry and correctly configure the system settings with the help of Reimage Repair Tool if that is the cure. For more information about the steps of using that tool with screenshots, please refer to 3TB external suddenly becomes 746GB.

Another possible explanation is that you are using Intel RST version of This type of Intel RST makes Windows operating system ignores the about 2.2TB of raw capacity of the 3TB HDD. Therefore, Disk Management only recognizes the left 746GB disk space. To fix the issue on 3TB HDD, you need to upgrade Intel RST to 10.1 or newer version. Then, you may be able to utilize the full size.


When you find 3TB HDD not showing full capacity in Windows 7 or Windows 10, don’t be panic. Obtain the corresponding fixes for your issue. Besides, AOMEI Partition Assistant is also a good help in solving unallocated space on 4TB hard drive issue.