FOTR discusses the forensic study of the skeletons' heights.
For Olga, it says "When Maples went to examine the remains to estimate height, he found that the leg bones - one of the primary indicators used to gauge how tall a person may have been - had been cut into sections by the Russians. He was forced to measure the bones of the arms, a less reliable method, and estimated her height at roughly 64.9 inches" (pg. 424). So according to this more unreliable method, her height was 5'4" - nearly 5'5".
It also says, "Of the sisters, Tatiana seems to have been the tallest, though Marie had come close as her final growth cycle was completed. They seem to have been within an inch or two of each other. Olga was somewhat shorter than both, perhaps by as much as two or three inches. None of the sisters, however, was as short as Anastasia, who was several inches shorter than Olga" (pg. 428).