5’6”, according to Wikipedia, which is tall from my perspective ;-). She’s 86 now. A great talent who had a very solid career for decades. Mother was a ballerina, father was a musician, so a stage career was a pretty obvious outcome.
Think about how Cyd Charisse (another beautiful star, but not the talent of Gaynor) towered over Astaire, Gene Kelly, and other leading men—something you didn’t notice unless dancing. They would put Charisse in flats and maneuvered choreography to downplay her height. These days, tall is beautiful. As in 6ft Melania.