Head over to IMC Broker’s blog to find a really good guide to tanker sizes. From Handy to ULCC this guide has pictures, descriptions and dead weight tonnages to help you visualize the different sizes. An example:

Capesize: Refers to a rather ill-defined standard which have the common characteristic of being incapable of using the Panama or Suez canals, not necessarily because of their tonnage, but because of their size. These ships serve deepwater terminals handling raw materials, such as iron ore and coal. As a result, “Capesize” vessels transit via Cape Horn (South America) or the Cape of Good Hope (South Africa).

LINK : IMC’s Tanker Sizes Guide

If your not a professional mariner you might also want to take a look at their Shipboard Chain of Command Guide.