Which convention this page uses, and how to switch
The page opens on the decimal convention that the SI system defines: a gigabyte is 1,000 megabytes. That is the one on drive packaging, in macOS and in network and plan figures. The binary convention divides by 1,024 and uses the names mebibyte (MiB) and gibibyte (GiB). It is how memory is sized and how Windows counts, although Windows labels the result MB and GB.
The buttons above the result switch between the two, and the list below the result always shows both. 1,024 MB is 1.024 GB on the decimal convention, while 1,024 MiB is exactly 1 GiB on the binary one, which is the clearest example of why the answers differ.
The formula and worked examples
- 250 MB is 0.25 GB decimal. 250 MiB is 0.244140625 GiB binary.
- 1,500 MB is 1.5 GB decimal.
- 4,096 MiB, a common memory size, is exactly 4 GiB binary, which is why a 4 GB stick of RAM is really 4 GiB. Read as 4,096 MB it would be 4.096 GB decimal.
- 25 MB, the attachment limit on many email services, is 0.025 GB.
The decimal answer always has the digits of the megabyte number shifted three places. The binary answer needs a real division, so it often has a long decimal tail. The table under the converter runs from 1 to 8,192 and gives the decimal answer (MB to GB) and the binary answer (MiB to GiB) on each row.
MB or Mb? A bit is not a byte
Speeds and some plan sizes are written in megabits, with a lowercase b. Eight bits make a byte, so 1 megabyte is 8 megabits, and 1,000 megabits is 125 megabytes. Dividing 1,000 Mb by 1,000 to get 1 Gb is a valid conversion between bits, but it does not give you 1 GB. Check the letter before you start.
When the number matters
Rounding a file to the nearest gigabyte is harmless, but a limit can be exact. An upload that must be under 1 GB should be under 1,000 MB to be safe, since some systems count 1 GB as 1,000 MB and others count 1 GiB as 1,024 MiB, often still called GB and MB. If a limit or a quota decides what you can do, use the smaller, decimal reading.