Bald eagle nests are generally 4-5 feet wide and 2-4 feet deep, although the nesting pair will add nesting material to the nest every year. Some eagle nests stay small, but some can reach 10 feet across and weigh a thousand pounds! The largest recorded bald eagle nest, located in St. Petersburg, Florida, was 9.5 feet in diameter, 20 feet deep and weighed almost 6,000 pounds. Nests may grow so large that they make a tree top heavy, and will cause the nest or tree to fall over in storms.
U.S. Fish and Wildlife Services; https://www.fws.gov/midwest/eagle/Nhistory/biologue.html