Megabytes to gigabytes (MB to GB)

One megabyte is exactly 0.001 gigabytes. That is the definition of the prefixes, not a measurement: the decimal SI prefixes (kilo, mega, giga, tera) step by exactly 1,000, and the binary IEC prefixes (kibi, mebi, gibi, tebi) step by exactly 1,024. The two families are both exact; the trouble is only that software and storage labels do not always say which one they mean.

Worked through: 512 MB x 0.001 = 0.512 GB.

Going the other way, one gigabyte is 1,000 megabytes.

For mental arithmetic: Move the decimal point three places left.

A thousand, not 1,024. Which one is right depends on who is talking. The SI prefixes are decimal, so a megabyte is 10^6 bytes and a gigabyte 10^9, which is what drive manufacturers use and what this converter follows. Operating systems have historically used 1,024-based units while still calling them MB and GB, which is where the whole confusion comes from. The unambiguous binary units are the mebibyte and gibibyte, and they are on this converter too.

Precision is worth matching to the input. A measurement given as 100 MB carries one or two significant figures, and reporting its conversion to six implies a precision the original never had.