7.5 in
There seems to be no legends pertaining to the naming of Pegasus. According to the Greek poet/writer Hesiod the name Pegasos was the word for "spring" or "well" and this is in accordance with myths...
He was born from a drop of blood that fell from Medusa's neck when Perseus beheaded her, Perseus then flew home on him.
No sister, but a brother, the giant Chrysaor.
He arose from the blood that dripped from Medusa's severed head.