Question : Zip Code Radius Calculation C# SQL MySQL

I have found http://www.experts-exchange.com/Database/GIS_and_GPS/Q_23725276.html and understand the 1 degree per 60 nautical miles calculation somewhat.  If I want to see a five mile radius how do I utilize the calculation?

The programming language is C# and database used is MySQL.  I want to look up all zip codes within a certain radius (generally five miles) of a specific zip code.  Samples for distance calculation are plentiful but radius calculation doesn't seem to be so simple.  Any help on this is greatly appreciated.

Answer : Zip Code Radius Calculation C# SQL MySQL

I don't know which is correct.  Here is a post I found that uses yet another calculation
http://www.meridianworlddata.com/Distance-Calculation.asp