What does this tool do?
Drives are sold using decimal units, but operating systems often report binary units, so a 1 TB drive appears as roughly 931 GiB. This calculator shows that difference and lets you reserve space for formatting overhead.
The Formula
Usable bytes = Advertised bytes × (1 − reserve %); reported TiB = usable bytes ÷ 2^40Frequently Asked Questions
Is my drive missing storage?
No. The bytes are all there; the operating system is counting them in larger binary units. A 1 TB drive holds 1,000,000,000,000 bytes, which is 931.32 GiB.
How much space should I reserve?
Filesystems, partition tables and over-provisioning can consume a few percent, and keeping 10–15% free helps performance. Enter a reserve that matches how you plan to use the drive.