Thus was he handled for one year and ten months; after which time, by the advice of physicians, they began to carry him, and then was made for him a fine little cart drawn with oxen, of the invention of Jan Denio
This is a good representation of the size of the giant, even at a very young age he was huge, "little cart drawn with oxen" is a visual representation on how big he really is. However throughout many tales Gargantua varies in size in different stories, and even in different parts of the same stories. In some parts, the giant stands about 300 feet tall, but seems to reach heights up to 1,000 feet throughout the tale.