Units
Why does a 1 TB drive show only 931 GB?
931.3GB in Windows
for a drive sold as 1 TB: the same bytes, counted in powers of 1,024
Nothing is missing. The drive maker counts in powers of 1,000, as the SI prefixes define. Windows counts in powers of 1,024 and still labels the result "GB".
The arithmetic
- 1 TB = 1,000,000,000,000 bytes (the maker's decimal count)
- 1 GiB = 1,024 × 1,024 × 1,024 = 1,073,741,824 bytes
- 1,000,000,000,000 ÷ 1,073,741,824 = 931.32 GiB
- or ÷ 1,024 again = 0.909 TiB; Windows shows it as “0.90 TB”
- The number looks 9.1 % smaller, with every byte still there
| Sold as | Windows shows | Looks smaller by |
|---|---|---|
| 16 GB | “14.9 GB” | 6.9 % |
| 32 GB | “29.8 GB” | 6.9 % |
| 64 GB | “59.6 GB” | 6.9 % |
| 128 GB | “119.2 GB” | 6.9 % |
| 256 GB | “238.4 GB” | 6.9 % |
| 512 GB | “476.8 GB” | 6.9 % |
| 1 TB | “931.3 GB” | 6.9 % |
| 2 TB | “1.81 TB” | 9.1 % |
| 4 TB | “3.63 TB” | 9.1 % |
| 8 TB | “7.27 TB” | 9.1 % |