I need to upload a file listed as 50,827 KB to a site with a maximum upload capacity of 100MB per file... by my way of thinking the file to be uploaded is 50.8MB and thus able to upload - right?

There are two views about how to quantify a megabyte or a kilobyte.

In SI units, mega means 1,000,000; kilo means 1000. So, a megabyte would be 1,000,000 bytes and a kilobyte would be 1,000 bytes.

In common usage among programmers, a kilobyte is 1024 bytes (2^{10}) and a megabyte is 1024 kilobytes (2^{20}=1048576\, bytes)

So, the answer to your question must depend on which usage you are using. Since I don't know the context, I can't answer accurately.

You don't need to convert this exactly. It is approximately 50.8MB, about half your limit. So yes you're safe.