Why does my 1 TB drive show 931 GB?

Nothing is missing. Drive makers count 1 GB = 1,000,000,000 bytes; Windows counts 1 GB = 1,073,741,824 bytes. Enter your drive size to see what you will get.

Exact size:

Windows shows:

macOS shows (decimal since 10.6):

Unit converter

Where the “missing” space goes

  1. Units (the big one): 1 TB on the box = 1,000,000,000,000 bytes = 931.3 GiB. Windows labels GiB as “GB”, so you see 931 GB. The bigger the drive, the bigger the gap: about 7% for GB, 9% for TB.
  2. Formatting: the file system uses a little space for its own tables.
  3. Recovery and system partitions: on a new PC, the factory recovery partition can take several GB more.
  4. Consoles and phones: the operating system itself is counted as used space.

When it really is a problem

If a drive shows a tiny fraction of its size (for example a “1 TB” stick showing 32 GB), the partition may be wrong, or the drive may be counterfeit with fake capacity. Back up what is on it before reformatting or testing it.

Questions

Does macOS show the full 1 TB?

Yes. Since Mac OS X 10.6, Finder uses decimal units like the drive makers, so it shows about 1 TB (minus formatting).

Is GiB the same as GB?

No. 1 GiB = 1,073,741,824 bytes, 1 GB = 1,000,000,000 bytes. RAM is usually sold in GiB even when labelled GB.

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