A location is considered to be a desert if it gets less than 10 inches, or 25 centimeters, of rain a year. Some locations may get less than 1 centimeter, or less than one-half of an inch, of moisture per year.
The geological definition of a desert is an arid region that gets less than 10 inches of precipitation with a yearly evaporation rate that is more than 10 inches a year. Deserts are not always hot, and only about 10 percent of them have sand and dunes.
The hottest deserts tend to have the least amount of rain, with the Atacama Desert in Chile averaging about 1.5 centimeters of rain each year, but some years see no precipitation at all. The inland regions of the Sahara also see only about 1.5 centimeters of rain. Hot deserts in the United States get less than 28 centimeters of rain a year.
Semiarid deserts across the world, and those found in the Great Basin, Montana and Utah, get between 2 and 4 centimeters of rain a year. Dew provides almost as much moisture as rainfall does in these areas. Coastal deserts see about 8 to 13 centimeters of rain, but some can get as little as 5 centimeters. Chile has coastal deserts along the west coast. Cold deserts, such as those found in Antarctica, get snow as their precipitation. They average about 15 to 26 centimeters per year.