A new drive advertised as 1 TB may appear as roughly 931 GiB in a file browser. That is normally not a missing chunk of storage or a defective device; it is a disagreement over prefixes. Drive manufacturers use decimal SI prefixes, where 1 TB is 1,000,000,000,000 bytes. Many operating systems historically display that byte count with binary multiples of 1,024, even when they label the result TB. The number changes, but the underlying bytes do not.
Decimal Prefixes and Binary Prefixes
In the decimal system, 1 kB is 1,000 bytes, 1 MB is 1,000,000 bytes, 1 GB is 1,000,000,000 bytes, and 1 TB is 10^12 bytes. The technically precise binary names are kibibyte (KiB), mebibyte (MiB), gibibyte (GiB), tebibyte (TiB), and pebibyte (PiB): each step is 1,024 times larger. Thus 1 TB equals approximately 931.323 GiB, while 1 TiB equals 1,099,511,627,776 bytes.
Bits and bytes create a second source of confusion. A byte is eight bits, so an internet connection advertised at 1 gigabit per second is not a 1 gigabyte-per-second download. Divide the bit rate by eight first, then account for protocol overhead and the difference between decimal and binary reporting. The Data Storage Converter lets you choose the interpretation explicitly rather than guessing from a label.
Why the Difference Grows With Capacity
The percentage difference between decimal and binary prefixes is about 2.4% at the kilobyte step and about 7.4% at the terabyte step. It is not that a manufacturer has taken 69 GB from a 1 TB drive; the same 1,000,000,000,000 bytes are being divided by 1,073,741,824 bytes per GiB. Formatting, a recovery partition, and the file system can reduce the usable figure further, but those are separate effects.
Convert Before You Compare
When comparing a backup target with a source, convert both values to bytes or to the same named prefix. Use the Numbers Converter to inspect large byte counts in decimal or hexadecimal when troubleshooting a protocol or file header, and use the Percentage Calculator to quantify the difference between two capacity reports. Clear units turn an apparently mysterious storage mismatch into straightforward arithmetic.