And you might confuse MB, megabytes, with MiB, mebibytes. MB is typically used to measure storage, and MiB typically used to measure data. There's 1000 bytes in a kilobyte, and 1024 bytes in a kibibyte.
I still use mb and kb as 1024 instead of 1000, because I prefer to not have units switched around from under me. 2^16 will always address 64kb, not 65.
KB is measured in powers of 10, where KiB is measured in powers of 2:
However, this error is so common that most folks will know what you mean. It'll only really get you in trouble when you're accurately comparing sizes of storage and data. There's a good chance it won't really matter unless you're working with code or archiving disks.
This is also why a "2 TB" hard drive is "smaller than 2 TB." 2 terabytes is 1.819 tebibytes. Even Windows will incorrectly call TiB units TB and terabyte, so people have often carried a conspiracy theory that drive manufacturers "short you," or that the missing data somehow has to do with enormous file system metadata.
There are actually two standards here. Kibibytes was introduced later as a way to reduce confusion cause by the uninitiated thinking the JEDEC standard refered to powers of ten instead of two. That's why I'm saying that 64 kilobytes is equal to 2^16 bytes, because that's what the original standard was.