How to determine the size of the fixed VHD based on the remaining capacity of the physical hard disk?

Dear All,

I want to configure a fixed VHD based on the remaining capacity of my unused capacity on the Physical Hard Disk.

I am a bit confused here as to how to determine and indicate the size of a fixed VHD based on my remaining capacity of my physical Hard Disk under Hyper-V.

Eg,

I am using a Seagate 2TB SAS hard disk.

Under My Computer, it shows 244GB for Drive C: and 1.58TB for Drive D:

Under the drive properties of each, it indicates:

262,038,089,728 bytes for Drive C: (244GB)

1,738,252,742,656 bytes for Drive D: (1.58TB)

In order to fully utilize the unused space of 1,738,252,742,656 bytes, how do I specify in GB in HYPER-V Settings?

I tried the following configuration:

I specify 1580GB, it remains 20GB spare space in HYPER-V (Storage-> Disk Management)

If I specify 1700GB, it shows 120GB spare space remaining in HYPER-V (Storage-> Disk Management)

(This is a bit weird because, if I were to specify 1600GB, in theory it should fully utilize the physical capacity of the hard disk, however by specifying a value 1700GB, it actually reflect a 120GB spare space remaining).

(What will happen if physical data exceeds the 

So what is the exact value I should specify?

Pleas advise and thanks.

Alvynng