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Why does a 2 TB drive show 1.81 TB?

1.81TB in Windows

for a drive sold as 2 TB: the same bytes, counted in powers of 1,024

The gap between decimal and binary grows with each prefix: 2.4 % at kilo, 7.4 % at giga, 10 % at tera. A 2 TB drive shows about 9 % less than its label in Windows.

The arithmetic

  1. 2 TB = 2,000,000,000,000 bytes (the maker's decimal count)
  2. 1 GiB = 1,024 × 1,024 × 1,024 = 1,073,741,824 bytes
  3. 2,000,000,000,000 ÷ 1,073,741,824 = 1,862.65 GiB
  4. or ÷ 1,024 again = 1.819 TiB; Windows shows it as “1.81 TB”
  5. The number looks 9.1 % smaller, with every byte still there
What other sizes show in Windows
Sold asWindows showsLooks 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 %

Try your own numbers in the gb vs gib calculator

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