How many MB are in 18.2 GB

This depends on what you are talking about. The standard definition of 1GB is 1,024MB. So 18.2GB = 18636.8MB.

However, Hard Drive Manufactures round this to 1000MB in a GB, so you only get 18200MB.

by putting an i in the middle (e.g. Mib) you specifically define the 1,024 step, not the 1,000 rounding (so 18.2GB = 18,636.8MiB and 18,636.8MB and 18,200MB)

By the way, MiB is Mibibytes, whereas MB is megabytes!