It can be really frustrating to find out that a hard drive you have just purchased doesn’t actually contain the claimed storage space but rather a lot less. You would think that a 1TB drive should provide you with a 1TB of actual storage space. While this is a correct assumption, the claimed storage capacities are not technically incorrect.

hard-driveHard Drive Storage Capacity Calculations

The reason for this discrepancy lies in the way manufacturers and computers calculate storage capacity. Hard drive manufacturers calculate it using the decimal system (base 10), therefore, for them, 1 Megabyte is equal 1000 Kilobytes, 1 Gigabyte is equal 1000 Megabytes, and 1 Terabyte is the same as 1000 Gigabytes. However, computers and RAM manufactures use the binary numeral system (base 2) to calculate storage space, which means computer memories are counted by groups of 1024 so for them, a 1 MB is really 1024 kilobytes, a 1GB is 1024MB, and a 1 TB is 1024GB. Since the end users are mostly familiar with the decimal system, drive manufacturers use it to their advantage when marketing their storage media.

Hard Drive Formatting

An additional layer of storage reduction kicks in when you format your new hard drive. Once you do, the drive’s usable storage space is further reduced, although not by a lot. The actual amount by which the space is reduced depends on the file system (NTFS, FAT32, HFS, XFS, etc.) you format it to. Since a drive can be formatted into various file systems, it is unreasonable to expect hard drive manufacturers to advertise the actual storage capacity after the hard drive is formatted.

Will the Recovered Data Fit on the Destination Hard Drive?

As a data recovery company we witness the confusion that this capacity discrepancy causes on a daily basis. At the end of each successful recovery our clients get to choose if they provide us with a healthy destination hard drive to transfer the recovered data onto or purchase one from us. Oftentimes confusion occurs when we tell them that their spare drive they have provided us with does not actually have enough free space to transfer the recovered data.  For instance, if we recover 2TB of data, a new 2TB hard drive will not fit the entire recovered data, as in fact this hard drive only contains around 1.86TB of usable space.

To help you further understand this, the table below shows a few examples of the discrepancies between the claimed and actually usable hard drive storage spaces:

Claimed Space  Actual Space Difference
32GB 29.8GB 2.2GB
100GB 93.13GB 6.87GB
250GB 232.83GB 17.17GB
500GB 465.66GB 34.34GB
1TB 931.32GB 92.68GB
2TB 1862.64GB 185.36GB


Always expect your new hard drive to contain less usable storage space than advertised, especially once the drive is formatted. Even though there is a discrepancy between the advertised and actual storage space, which may at first be portrayed as misleading information, drive manufactures are not technically wrong in their claims. They simply use the decimal system to measure hard drive storage space versus the binary one. To avoid running out of space, next time you shop for a new drive, always get a bigger capacity hard drive than what you actually need to store or back up your data.