Bits, bytes, decimal and binary units
A byte is 8 bits. Larger sizes come in two families. The decimal units KB, MB, GB and TB step up by 1,000, like other metric prefixes. Drive makers, phone makers and network speeds use them. The binary units KiB, MiB, GiB and TiB step up by 1,024, which matches how computer memory is addressed.
Windows shows sizes in binary units but labels them KB, MB and GB, which is why a new 1 TB drive appears as about 931 GB there. macOS and most phones use decimal units, so the same drive shows as 1 TB.
Internet speeds are given in bits per second. Divide Mbps by 8 to get megabytes per second: a 100 Mbps connection downloads at most about 12.5 MB per second.
Common data size conversions
| From | Equals |
|---|---|
| 1 gigabyte | 1,000 megabytes |
| 1 terabyte | 1,000 gigabytes |
| 1 terabyte | 931.3225746 gibibytes |
| 1 gibibyte | 1.073741824 gigabytes |
| 1 megabyte | 0.9536743164 mebibytes |
| 1 byte | 8 bits |
| 1 gigabyte | 8,000,000,000 bits |
Advertised drive size to binary GiB
| Gigabytes (GB) | Gibibytes (GiB) |
|---|---|
| 16 | 14.901 |
| 32 | 29.802 |
| 64 | 59.605 |
| 128 | 119.21 |
| 256 | 238.42 |
| 500 | 465.66 |
| 512 | 476.84 |
| 1,000 | 931.32 |
| 2,000 | 1,862.6 |
| 4,000 | 3,725.3 |
Where the conversions come up
You meet it when a 128 GB phone has 119 GB free out of the box, when a 4.7 GB movie will not fit on a "4 GB" USB stick, or when an upload form says the file size limit is 25 MB and your photo is 26,214,400 bytes. Download times are another one: a 50 GB game on a 100 Mbps line is 50,000 megabytes at 12.5 megabytes per second, so a little over an hour.
Shortcuts: for decimal units move the decimal point three places per step. For binary units multiply by 1,024 each step, or take 93 percent of the decimal number for a rough binary figure (1,000 GB is about 931 GiB). And 8 bits make a byte, so divide any speed in megabits by 8 to get megabytes.
How to use it
- 1Pick the unit on the label or in the error message on the left, and the unit you want on the right. Decimal (GB) and binary (GiB) units sit next to each other in the list.
- 2Type the size. Either side works, and swap reverses the conversion.
- 3Read the result and the list of every other unit below it, from bits to tebibytes. Copy the value or a link.
Frequently asked questions
Why does my 1 TB drive only show 931 GB?
The drive has 1,000,000,000,000 bytes, which is 1 TB in decimal units. Windows divides by 1,024 three times and shows 931 GiB, but labels it GB. No space is missing.
Is a kilobyte 1,000 or 1,024 bytes?
Officially 1,000. The 1,024-byte unit is called a kibibyte (KiB). In practice, many programs still use KB for 1,024 bytes.
What is the difference between Mbps and MB/s?
Mbps is megabits per second, MB/s is megabytes per second. One byte has 8 bits, so 8 Mbps equal 1 MB/s.
How many megabytes are in a gigabyte?
1,000 MB in decimal units, or 1,024 MiB in a GiB in binary units.
How many bytes are in a megabyte?
1,000,000 bytes. The binary cousin, a mebibyte (MiB), has 1,048,576 bytes, and many programs label that MB too.