According to 1 Samuel 17:4, Goliath was 6 cubits and a span (according to the Masoretic text/Hebrew translation), equating to nine feet and six inches. This is incredibly tall, surpassing the tallest man recorded to date who measured 8 feet and eleven inches. Now while 9’6 is a very great height, it is not that unbelievable in comparison with this man. If God created a man a nine-foot-tall without the same intrinsic purpose as he used Goliath’s height, six inches is an honestly conservative amount to add in order for God’s purpose to be accomplished through this formidable man.
On top of this already being perfectly reasonable for God to make a man of this height, there is also wiggle room within a cubit. A cubit is the length from an elbow to a fingertip. From person to person this will vary, so Goliath could have actually been a few inches shorter than this recorded height. Regardless, Goliath’s height is nothing too unreasonable, and we are able to have confidence in it as biblical truth.