A king is the ruler of a large kingdom whereas a prince is the ruler of a smaller area or principality. The word "prince" is also used to describe the son of a king or emperor.
Comparison chart
 | King | Prince |
|---|---|---|
| Female ruler | The female form is known as Queen. She can be the wife or mother of the King, or ruler of the Kingdom. | The female form is the princess. She can be the daughter of the king & queen, or wife of the prince, or ruler of the principality. |
| Source of power | Inheritance, by conquest or elected | Inheritance |
| Modern rulers | The King of United Kingdom is an example. | The Prince of Wales is an example. |
| About | A king rules a kingdom, might be a part of an empire. | A ruler of a principality. |
| Divine status | Like Emperors, Kings may be considered Gods within their own Kingdom, alternatively they may reign by the Grace of God. | Usually the son of an emperor, king, or ruling/crown prince. |
| Power | For some power of Kings maximum in his kingdom, for others they may be vassels to a greater monarch. Some Kings, such as those in France and Britian ruled over far greater terretories than most Emperors. | The prince's power is restricted to his province. |
| Politics | Each kingdom has its boundary and it’s own politics and a king is the ruler that kingdom. Often a King will rule over several Kingdoms in a personal union, some such as the Kings of Great Britain also held the substitutiary title of Emperor of Indi | Each principality has its boundary and it's own politics. |
Emperor 
Emperor
Comments: King vs Prince