Which convention this page uses, and how to switch
The page opens on the decimal convention: 1 gigabyte is 1,000 megabytes, so you multiply by 1,000 and the digits barely change. The binary convention multiplies by 1,024 and uses the names gibibyte (GiB) and mebibyte (MiB). When you multiply, the binary answer comes out larger than the decimal one: 2 GiB is 2,048 MiB, and 2 GB is 2,000 MB.
The two buttons above the result switch convention, and the list below the result always shows both answers.
Data plans and upload limits
Mobile plans and cloud storage are often sold in GB and used in MB, so this conversion comes up when you check usage. A 5 GB plan is 5,000 MB with the decimal convention. Counted in binary, the same 5 is 5 GiB, which is 5,120 MiB. The two are not the same amount of data, because a GiB is bigger than a GB: 5 GiB is 5,368.7 MB, about 369 MB (7.4%) more than 5 GB. Some providers count one way and some the other, so read the terms before you trust either.
Upload limits are the other common case. A form that allows files up to 2 GB might count that as 2,000 MB or as 2,048 MiB (2 GiB). If a file is close to the limit, treat the limit as 2,000 MB. A file at 2,010 MB might upload on one system and fail on another.
Storage tiers and memory
Drives, phones and memory cards come in tiers such as 32, 64, 128 and 256 GB, counted in decimal by their makers. A 32 GB card holds 32,000 MB, which is 30,517.6 MiB or 29.8 GiB, and that is the figure an operating system that counts in binary will show. Memory is the opposite: 8 GB of RAM is 8 GiB, which is 8,192 MiB. The data storage converter has a card that works out what any drive size looks like in Windows.
Quick mental versions
For decimal, shift the decimal point three places to the right: 1.25 GB is 1,250 MB. For binary, multiply by 1,000 and then add about 2.4% (24 per 1,000): 1 GiB is 1,024 MiB, and 4 GiB is 4,096 MiB. That 2.4% is only the gap between the two multipliers, 1,000 and 1,024. The units themselves differ more: a MiB is 4.9% bigger than a MB and a GiB is 7.4% bigger than a GB, so 5 GiB exceeds 5 GB by about 369 MB.