Type a size and pick the units. Decimal units (GB) and binary units (GiB) are both listed, which explains most "missing" disk space.
1 TB = 931.32257 GiB
In all units: 1 TB
Bits
8,000,000,000,000 bit
Bytes
1,000,000,000,000 B
Kilobytes
1,000,000,000 kB
Megabytes
1,000,000 MB
Gigabytes
1,000 GB
Terabytes
1 TB
Petabytes
0.001 PB
Kibibytes
976,562,500 KiB
Mebibytes
953,674.32 MiB
Gibibytes
931.32257 GiB
Tebibytes
0.9094947 TiB
Megabits
8,000,000 Mbit
Gigabits
8,000 Gbit
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How it works
Every unit is stored as a number of bytes. There are two families:
Decimal (SI)
Bytes
Binary (IEC)
Bytes
Kilobyte (kB)
1,000
Kibibyte (KiB)
1,024
Megabyte (MB)
1,000,000
Mebibyte (MiB)
1,048,576
Gigabyte (GB)
1,000,000,000
Gibibyte (GiB)
1,073,741,824
Terabyte (TB)
10¹²
Tebibyte (TiB)
1,099,511,627,776
The gap grows with each step: a KiB is 2.4% bigger than a kB, but a TiB is almost 10% bigger than a TB.
Who uses what: storage makers, macOS, iOS and Android use decimal units. Windows shows binary sizes but labels them “KB”, “MB” and “GB”. Memory (RAM) is always sized in binary units.
Bits measure transfer speeds: 1 byte = 8 bits, so 1 Mbit = 125 kB.
Examples
New drives. 1 TB is 931.32 GiB; 2 TB is 1.819 TiB; 500 GB is 465.66 GiB.
Phones. A “256 GB” phone has 238.42 GiB of raw storage before the system takes its share.
Internet. 100 Mbps is 12.5 MB/s, so a 1 GB download takes at least 80 seconds.
Frequently asked questions
Why does my 1 TB drive only show 931 GB?+
Drive makers count in decimal units, where 1 TB is 1,000,000,000,000 bytes. Windows counts in binary units, where a "GB" is really 1,073,741,824 bytes (a GiB). The same number of bytes is 931.32 GiB, so no space is missing.
Is a kilobyte 1,000 or 1,024 bytes?+
Officially, a kilobyte (kB) is 1,000 bytes and a kibibyte (KiB) is 1,024 bytes. Some software still uses "KB" to mean 1,024 bytes, which is where the confusion comes from.
What is the difference between Mbps and MB/s?+
Internet speeds are in megabits per second (Mbps); file sizes and download speeds in browsers are in megabytes. A byte is 8 bits, so a 100 Mbps connection downloads at most 12.5 MB per second.
How long does it take to download a file?+
Convert the file size to megabits and divide by your connection speed. A 1 GB file is 8,000 megabits, so at 100 Mbps it takes at least 80 seconds.