Why does my 1 TB hard drive show less space in Windows?

Hard drive manufacturers use SI decimal definitions where 1 TB = 1,000,000,000,000 bytes (10^12). Windows reports storage using binary definitions where 1 TiB = 1,099,511,627,776 bytes (2^40). So a 1 TB drive contains about 931 GiB as reported by Windows. The actual storage capacity is unchanged; only the labelling convention differs.

What is the difference between GB and GiB?

GB (gigabyte) in the SI system equals 1,000,000,000 bytes (10^9). GiB (gibibyte) in the IEC binary system equals 1,073,741,824 bytes (2^30). One GiB is about 7.37 percent larger than one GB. Storage manufacturers use GB; operating systems like Windows traditionally use GiB but label them GB, which causes the apparent discrepancy.

How many bits are in a byte?

There are 8 bits in one byte, by universal definition. This relationship is constant across both SI and binary systems. A kilobit (kbit) therefore equals 125 bytes, and a megabit (Mbit) equals 125,000 bytes. Internet speeds are often quoted in megabits per second (Mbps) rather than megabytes, so a 100 Mbps connection downloads at roughly 12.5 MB/s.

Data Storage Converter

This data storage converter converts between the most common digital storage units in both the SI decimal system and the IEC binary system: bits, bytes, kilobytes (KB), megabytes (MB), gigabytes (GB), terabytes (TB), petabytes (PB), kibibytes (KiB), mebibytes (MiB), gibibytes (GiB), and tebibytes (TiB). The distinction between SI and binary matters because storage hardware manufacturers use SI definitions where 1 GB equals exactly 1,000,000,000 bytes, while operating systems like Windows have traditionally reported storage using binary definitions where 1 GiB equals 1,073,741,824 bytes. This is why a hard drive labelled 1 TB appears as approximately 931 GiB in Windows. The converter uses bits as its internal reference: all inputs are converted to bits using exact multiplication, and all outputs are derived from that bits figure. Eight bits make one byte, and all other conversions follow exactly from there. You select the unit you are starting from, enter a value, and all ten other equivalents appear immediately in both columns. The tool is useful for understanding why a drive appears smaller than labelled, for comparing file size specifications across different platforms, for network bandwidth calculations (which use bits), and for storage planning. This tool does not distinguish between decimal kilobytes (1,000 bytes) and the older ambiguous KB that sometimes meant 1,024 bytes; it follows the IEC 80000-13 standard strictly for binary prefixes.

From unit

Value to convert

1000.0000

megabytes (MB)

bits8,000,000,000

bytes1,000,000,000

KB1,000,000

MB1,000.00

GB1.0000

TB0.001000

PB1.0000e-6

KiB976562.5000

MiB953.6743

GiB0.9313

TiB0.000909

How it works

The converter converts all inputs to bits first: 1 byte = 8 bits; 1 KB = 8,000 bits; 1 MB = 8,000,000 bits; 1 GB = 8,000,000,000 bits; 1 TB = 8,000,000,000,000 bits; 1 PB = 8 x 10^15 bits; 1 KiB = 8,192 bits; 1 MiB = 8,388,608 bits; 1 GiB = 8,589,934,592 bits; 1 TiB = 8,796,093,022,208 bits. All output values are derived by dividing the total bits by each unit's factor. SI units use powers of 10 and binary (IEC) units use powers of 2.

Worked example

Starting from 1 GB: 1 times 8,000,000,000 gives 8,000,000,000 bits. Dividing by 8 gives 1,000,000,000 bytes. Dividing by 8,000,000 gives 1,000 MB (SI). Dividing by 8,388,608 gives 953.67 MiB (binary). These match the default values pre-filled in the converter above.

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