KB, MB, GB, TB Explained (and Why Your Drive Shows Less Space Than the Box Says)
A 1 TB drive shows up as 931 GB on your computer. Nothing is missing — it's two different definitions of the same units. Here's the actual math.
By Piyush
Buy a drive labeled 1 TB, plug it into your computer, and it will almost certainly report something like 931 GB of usable space. This is one of the most-reported “bugs” in computing that isn't a bug at all — it's two industries using the same words to mean different numbers.
Decimal vs binary: the actual math
Storage manufacturers (drive makers, cloud providers) use decimal units, where each step is a clean multiple of 1,000, matching the metric system:
- 1 KB = 1,000 bytes
- 1 MB = 1,000,000 bytes
- 1 GB = 1,000,000,000 bytes
- 1 TB = 1,000,000,000,000 bytes
Operating systems, on the other hand, largely grew up around binary units, where each step is a power of 2 (1,024) because that maps naturally onto how memory and storage addressing actually works in hardware:
- 1 KiB = 1,024 bytes
- 1 MiB = 1,024 KiB = 1,048,576 bytes
- 1 GiB = 1,024 MiB = 1,073,741,824 bytes
- 1 TiB = 1,024 GiB = 1,099,511,627,776 bytes
The catch: Windows (and many other tools) label binary gibibytes as “GB” instead of the technically correct “GiB.” So when your 1,000,000,000,000-byte drive (a true decimal 1 TB) gets measured in 1,073,741,824-byte chunks and still called “GB,” you get 1,000,000,000,000 ÷ 1,073,741,824 ≈ 931 GB. The bytes are all there — it's purely a labeling mismatch between the box and the operating system.
Where this trips people up
- Buying storage: every advertised drive or SSD capacity will look 5–10% smaller once you plug it in. This is universal across every manufacturer and every operating system — it isn't a defect with a specific product.
- Cloud storage plans: most cloud providers use decimal units to match their marketing, so a “2 TB” plan is a true decimal 2 TB, but your OS may still display your usage of it in binary GiB, making the numbers look slightly different from what you'd expect.
- File size vs transfer time: internet speed calculations use decimal units (because that's how network speeds are specified), while your OS reports file sizes in binary units. Mixing the two without converting is a common source of “why is this taking longer than the calculator said” confusion.
The practical takeaway
You haven't lost storage, and nothing is wrong with your drive. When precision matters — sizing a backup, checking whether a file will fit, or converting between units for a transfer time calculation — use the file size converter, which handles both decimal and binary units explicitly so you're comparing the same kind of gigabyte on both sides.