One of the ways that I like to help students understand the size of a country or state is by showing them comparisons to states and countries with which they are familiar. For example, if I want my students to get a better sense of how big Utah is, I compare it Maine. The following three websites all make it easy for students to quickly compare the size of countries, states, and provinces.
Comparea.org offers a simple way to compare the size of countries, states, provinces, and cities. To make a comparison just choose two places from the drop-down menus on the right hand side of the screen. Along with the visuals your students can find links to World Factbook and Wikipedia entries about their chosen places.
MapFight. MapFight lets you select two U.S. states or two countries to quickly see which one is bigger and by how much. The select states or countries are put into overlays to help you see the size difference.
OverlapMaps is probably the most robust of the three sites on this list. Overlap Maps is a free service that can be used to quickly compare the size of countries, states, provinces, and some bodies of water. To create a visual comparison of two countries select one country from the “overlap this” menu and select one country from the “onto this” menu. The comparisons you make are displayed on a map. You can make comparisons from different categories.