Data Storage Converter
MB, GB, TB and their binary twins — both readings, side by side.
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1 GB = 1,000,000,000 bytes
The same size, read both ways
| Scale | Decimal (×1000) | Binary (×1024) | Gap |
|---|---|---|---|
| Kilo | 1,000,000 kB | 976,563 KiB | 2.4% |
| Mega | 1,000 MB | 953.674 MiB | 4.9% |
| Giga | 1 GB | 0.931323 GiB | 7.4% |
| Tera | 0.001 TB | 0.000909495 TiB | 10.0% |
| Peta | 0.000001 PB | 8.88178e-7 PiB | 12.6% |
Drives are sold in the decimal column. Windows, macOS Disk Utility’s older readings, and most programming languages report the binary column but label it with the decimal column’s names — which is where the missing space goes. It was never missing.
Broadband is advertised in megabits per second. Eight bits to a byte, so a 100 Mbps line moves about 12.5 MB per second at best.
to transfer 1 GB at 100 Mbps
A theoretical floor, not a prediction. Protocol overhead, the server’s own upload limit, and anything else sharing the line all push the real time higher.
1 GB in every other unit
- Bit (bit)8,000,000,000
- Kilobit (kbit)8,000,000
- Megabit (Mbit)
Broadband is sold in megabits per second, which is why a "100 Mb" line downloads at about 12.5 MB/s.
8,000 - Gigabit (Gbit)8
- Byte (B)1,000,000,000
- Kilobyte (kB)1,000,000
- Megabyte (MB)1,000
- Terabyte (TB)0.001
- Petabyte (PB)0.000001
- Kibibyte (KiB)976,562.5
- Mebibyte (MiB)953.6743
- Gibibyte (GiB)
What Windows and most tools call a "GB" when reporting a drive’s size.
0.9313226 - Tebibyte (TiB)0.0009094947
- Pebibyte (PiB)8.881784e-7
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How it works
To convert a data size, enter it above and pick its unit — the result is shown in your chosen unit and in both the decimal system drives are sold in (1 GB = 1,000,000,000 bytes) and the binary system operating systems report in (1 GiB = 1,073,741,824 bytes), which is the difference behind a 1 TB drive showing as 931 GB.
Digital storage has two unit systems that share their names, and almost every confusing number in computing comes from mixing them. The SI prefixes are powers of a thousand: a kilobyte is 1,000 bytes, a megabyte 1,000,000, a gigabyte 1,000,000,000. The IEC binary prefixes are powers of 1,024, which is the round number in base two: a kibibyte is 1,024 bytes, a mebibyte 1,048,576, a gibibyte 1,073,741,824.
Drive manufacturers sell in the decimal system. Windows, most file managers, and most programming languages measure in the binary system but label the result with the decimal names — so a drive holding exactly 1,000,000,000,000 bytes is divided by 1,073,741,824 and displayed as "931 GB". Nothing has been lost and no one is cheating; two systems are being used under one set of names. The gap widens at every step: 2.4% at kilo, 4.9% at mega, 7.4% at giga, 10% at tera.
The other factor of eight is bandwidth. Storage is counted in bytes and network speed is sold in bits, so a 100 Mbps connection moves at most 12.5 megabytes per second. That is why the download estimate on this page is not an extra — converting the file size is usually only half of the question someone came to answer. The estimate is a theoretical floor: protocol overhead, the far end’s upload limit, and anything else sharing the line all make the real time longer.
macOS is the exception worth knowing. Since OS X 10.6 it reports storage in decimal units, which is why the same drive shows as 1 TB on a Mac and 931 GB on a Windows machine.
Decimal and binary, compared
The same quantity of bytes under both systems. The right-hand column is what your operating system will usually show for a drive sold at the size in the left-hand column.
| Sold as (decimal) | Reported as (binary) |
|---|---|
| 500 GB | 465.66 GiB |
| 1 TB | 931.32 GiB |
| 2 TB | 1.819 TiB |
| 4 TB | 3.638 TiB |
| 8 TB | 7.276 TiB |
| 16 TB | 14.55 TiB |
Bytes in each unit
The exact definitions. Every conversion on this page is one of these divisions, which is why the numbers are exact rather than approximate.
| Unit | 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) | 1,000,000,000,000 |
| Tebibyte (TiB) | 1,099,511,627,776 |
Megabits and megabytes
Broadband is advertised in megabits per second and files are measured in megabytes, a factor of eight apart. Divide the advertised speed by eight for the best-case transfer rate.
| Connection speed | Best-case transfer |
|---|---|
| 10 Mbps | 1.25 MB/s |
| 50 Mbps | 6.25 MB/s |
| 100 Mbps | 12.5 MB/s |
| 500 Mbps | 62.5 MB/s |
| 1 Gbps | 125 MB/s |
FAQ
Why does my 1 TB drive only show 931 GB?
Because the drive holds 1,000,000,000,000 bytes — a decimal terabyte — and Windows divides by 1,073,741,824 to get gibibytes but labels the answer "GB". The drive has its full advertised capacity; the two systems simply share a name.
How many MB are in a GB?
1,000 MB in a decimal gigabyte, or 1,024 MiB in a binary gibibyte. Which one is right depends on who is doing the counting: a drive manufacturer means the first, an operating system usually means the second.
What is the difference between GB and GiB?
A gigabyte (GB) is 1,000,000,000 bytes; a gibibyte (GiB) is 1,073,741,824 bytes — about 7.4% more. The IEC introduced GiB in 1998 precisely to end the ambiguity, and storage and cloud vendors now largely use it in technical documentation even when their marketing does not.
How long will it take to download a file?
Enter the file size above and your connection speed in Mbps. The estimate divides by eight to convert bits to bytes and gives the theoretical best case — real transfers are slower because of protocol overhead and whatever else is using the connection.
Is a megabit the same as a megabyte?
No — a megabyte is eight megabits. A "100 Mb" broadband line downloads at about 12.5 MB per second at best. The lowercase b for bits and uppercase B for bytes is the only thing distinguishing them in writing.