How to Partition 3TB Hard Drive in Windows 11, 10, 8, 7

This post aims to tell why you cannot partition unallocated space on 3TB hard drive, and also introduce the best way to partition 3TB hard drive in Windows 11, 10, 8, 7.


By Cherry / Updated on May 12, 2023

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Can't partition unallocated space on 3TB hard drive



I have a Seagate 3TB hard drive, and I install Windows 10 on it. However, I forgot to partition hard drive at the beginning of the Windows installation. I used Windows Disk Management to create a 2TB partitions, and I was trying to create a another partition with the left unallocated space. But, when I right-click it, I found the “New Simple Volume” option is grayed out. So why and how can I partition this 3TB hard drive?"

3TB HDD Shows 2TB


Why you can't create a new volume with unallocated space on 3TB hard drive?

Why you cannot create a new partition with the unallocated space on 3TB disk? The problem is with the partition style. If you check the partition style, you will find it is MBR. MBR only supports up to 2TB hard drive. Namely, on a 3TB MBR-based hard drive, only the first 2TB hard drive is usable, the rest 1TB disk space will be shown unallocated in Disk Management, which be the main reason why many users find their 3TB HDD not showing full capacity.

How to partition 3TB hard drive to use the full size

The next part will explain to you the difference between MBR and GPT and how to partition 3TB hard drive successfully.


Now we know it is the MBR partition style that makes you unable to create a new partition with unallocated space on the 3TB hard drive. To fix this, we can change the MBR partition style to GPT. It is a new partition style, breaks out the MBR disk size limit and can support up to 9.4ZB. Check the following table to learn the difference between those 2 disk styles. Also, you can click What's the Difference Between GPT and MBR Partition Style to know more.


Then, here comes the problem: how to convert 3TB hard drive from MBR to GPT? Disk Management provides the conversion feature, but when you right-click the 3TB hard drive, you will find Convert to GPT Disk is grayed out. That’s because this tool can only convert an empty disk (without any partitions on) to GPT/MBR. Therefore, you have to delete all partitions before converting.

Convert to GPT Greyed Out

Best 3TB hard drive partition software

What if you don’t want to delete volumes you have created on the 3TB hard drive before converting it to GPT? Luckily, there is another option: apply the AOMEI Partition Assistant Professional software. It can convert disk to MBR or GPT without deleting any existing partitions on the disk, so the data wil be safe during the conversion. Next we will show how to convert a 3TB data disk as an example.

Download Demo Win 11/10/8.1/8/7/XP
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Note: GPT disk requires UEFI start mode. Before converting, you need to make sure that your motherboard supports UEFI boot mode if the 3TB MBR disk is the boot disk.

Step 1. Install AOMEI Partition Assistant Professional on your computer (You can download its demo version for a trial first). Launch it. It will display you the basic environment of your disk(s). Right-click the 3TB disk and select "Convert to GPT".

Convert 3tb Mbr Disk To Gpt

Step 2. It will ask you if you are sure to convert the selected disk from MBR to GPT disk. Click OK.

Ok 3tb Disk

If you installed system on the disk, it will give you a note that you should make sure if your motherboard supports EFI/UEFI boot. If not, your system will be unable to boot next time. If it supports, click Yes.

Step 3. Then, you will be back to the main interface, and you will see the disk has already become GPT disk. Click "Apply" to submit.

Apply 3tb

Wait till to proceed complete. After the conversion, you can use AOMEI Partition Assistant to create a new volume with unallocated space on 3TB hard drive.

1>. Right-click the unallocated space on 3TB hard drive, select "Create Partition".

Create Partition On 3tb

2>. Then, you can specify the partition size, drive letter, file system, partition type of your new partition. Click "OK".

Partition Detail

3>. Then, click "Apply" on the toolbar to submit the mission.



AOMEI Partition Assistant is such a great tool for users to partition 3TB hard drive and create a new volume with unallocated space on 3TB disk. It supports working with all Windows PC operating system including Windows 11/10/8/7. Besides, it provides you many other features such as resize partition, split partition, merge partitions, transfer OS to SSD and many more. For Windows Server users, the AOMEI Partition Assistant Server is a great tool.

Cherry · Staff Editor
Cherry is an editor of AOMEI Technology, she covers backup & restore, hard disk & partitions management, cloud files transfer, website & database backup and so on for AOMEI. She enjoys helping people find solutions to their problems. She loves traveling, cooking, reading and so on. She takes most of time with her family when she is not working.