Your drive shows less space mainly because manufacturers measure capacity in decimal units, where 1 GB equals 1,000,000,000 bytes, while Windows measures it in binary units, where 1 GB equals 1,073,741,824 bytes. A 1 TB drive really does hold a trillion bytes, but Windows displays that as about 931 GB. Formatting, hidden recovery partitions, and reserved system space then account for a little more.
Why this happens
There are two separate reasons, and the larger one is simply how the numbers are counted.
- Decimal versus binary counting. Drive makers define a gigabyte as 1,000,000,000 bytes and a terabyte as 1,000,000,000,000 bytes. Windows uses powers of two, where a gigabyte is 1,073,741,824 bytes. The physical bytes are identical; only the label differs. The gap grows with size and is about 7 percent on a 1 TB drive.
- Formatting and the filesystem. Creating a filesystem such as NTFS, exFAT, or APFS uses a small amount of space for the tables and structures that keep track of your files.
- Hidden partitions. New computers often ship with a recovery partition and system partitions that do not appear as usable space in your main drive view.
- Reserved space. Some systems set aside room for features like snapshots, virtual memory, or system restore.
Is this normal?
Yes, completely. Every drive from every brand behaves this way. A 1 TB drive reading as roughly 931 GB in Windows is exactly what you should expect, not a defect or false advertising.
Does it cause any problems?
No. You are not losing usable capacity beyond the small filesystem and partition overhead. The advertised bytes are all there; the difference you see is a labeling and rounding matter, not missing storage.
How to fix or check it
- Do the quick math. Multiply the advertised size by about 0.931 to see what Windows will report. A 2 TB drive shows around 1.86 TB, which is correct.
- Windows, see the real byte count: right-click the drive in File Explorer, choose Properties, and read the Capacity line in bytes. It will be very close to the advertised decimal figure.
- Windows, view all partitions: open Disk Management to see recovery and system partitions that are using part of the physical disk.
- Mac, check capacity: open Disk Utility and select the physical drive, or open About This Mac and then Storage. Modern macOS reports in decimal units, so it lines up more closely with the label.
- Confirm the drive is healthy: if the shortfall is far larger than 7 to 10 percent, look for a stuck format, an extra hidden partition you can reclaim, or a drive that was never fully partitioned.
Frequently asked questions
Why does my Mac show more space than my Windows PC for the same drive?
Because macOS reports capacity in decimal gigabytes that match the label, while Windows reports binary gigabytes. It is the same physical drive with the same bytes, just labeled by two different counting methods.
Can I get the missing space back?
The decimal versus binary difference cannot be recovered because it was never actually missing. You can, however, reclaim real space by merging or deleting an extra hidden partition or by assigning unallocated space to your main drive in Disk Management or Disk Utility.
Is a 1 TB drive showing 931 GB a defect?
No. That is the normal, correct result of Windows using binary units. If your drive shows dramatically less than that, then check for hidden partitions or a formatting problem.