Most of the Sahara is an area with an annual rainfall of less than 50 mm (2 in) /m2 and even less than 20 mm (0.8 in) /m2 near the Tropic of Cancer.

The lack of precipitation is more noticeable in the eastern Sahara, where the climate is more continental.

About 17% of the total area of the desert recieves an average of 5 mm (0.2 in) or less annual average rainfall.