Approximately 81,000 km^2

Photo from Wikimedia Commons
Namib Desert
The oldest desert on Earth, 55 million years of being dry/Deserts
The Namib Desert stretches along the Atlantic coast of southern Africa for over 2,000 kilometers, covering roughly 81,000 square kilometers of Namibia, Angola, and South Africa. At an estimated 55 million years old, it is considered the oldest desert in the world. Its sand dunes are among the tallest on Earth, with Big Daddy near Sossusvlei reaching about 325 meters. The desert is home to fog-basking beetles that drink condensation off their own backs, which is the kind of resourcefulness that would make a survivalist jealous.
Measurements
Roughly 2,000 km along the Atlantic
Approximately 55 million years
About 45 degrees C in the interior