List of Sphenisciformes by population

This is a list of Sphenisciformes species by global population. While numbers are estimates, they have been made by experts in their fields.
Sphenisciformes is the taxonomic order to which penguins belong. The IOC World Bird List recognizes 19 species of Sphenisciformes. BirdLife International has assessed 18 species, all of which have had their population estimated. This list follows IUCN classifications for species names and taxonomy. Where IUCN classifications differ from other ornithological authorities, alternative names and taxonomies are noted.
A variety of methods are used for counting penguins, including the first census from space in April 2012, when imagery from Ikonos, QuickBird-2, and WorldView-2 satellites were used to count emperor penguins in Antarctica. Most maritime surveys use strip transect and distance sampling to measure penguin species density; this is then extrapolated over the animal's range. The Galapagos penguin has been counted annually since 1961 by the Galápagos National Park Service. For more information on how these estimates were ascertained, see Wikipedia's articles on population biology and population ecology.
Extinct species from this order include the Waitaha penguin, which went extinct between 1300–1500, and the Chatham penguin, which is only known through subfossils; however, an extant individual may have been kept in captivity by researchers sometime between 1867 and 1872.