This is a list of Sphenisciformes species by global population. The numbers are estimates made by experts in their fields.

Sphenisciformes (from the Latin for "wedge-shaped") is the group to which penguins belong. The IOC World Bird List recognizes 19 species of Sphenisciformes. BirdLife International has assessed 18 species (95% of the total), and all of these have had their population estimated. This list uses IUCN classifications for species names and taxonomy. When IUCN classifications differ from other bird experts, alternative names and taxonomies are included.

Scientists use different methods to count penguins. One example is the first census from space in April 2012, when satellite images from Ikonos, QuickBird-2, and WorldView-2 were used to count emperor penguins in Antarctica. Most surveys on the ocean use strip transect and distance sampling to measure how many penguins are in an area. These results are then used to estimate numbers across the entire range of the species. The Galapagos penguin has been counted every year since 1961 by the Galápagos National Park Service. For more details about how these estimates are made, see Wikipedia's articles on population biology and population ecology.

Extinct species from this group include the Waitaha penguin, which disappeared between 1300–1500 (shortly after Polynesians arrived in New Zealand), and the Chatham penguin, which is only known from old bones. However, a living individual may have been kept in captivity by researchers between 1867 and 1872.