The largest owl in the world in terms of weight is the Blakiston's fish owl, a rare species found in Asia. The great gray owl is the longest owl. It weighs less than the Blakiston's fish owl.

Blakiston's fish owls can weigh up to 10 pounds and can have a wingspan of more than 6 feet. They can measure more than 2 feet long. Great gray owls, which are found in parts of North America, Europe and Asia, can be up to 33 inches long.

Russia, Japan and China have populations of Blakiston's fish owls. These owls hunt salmon for food. Little research has been done on them, because their small population and shy temperaments make it difficult for scientists to observe them.