The Bible does mention that there were some giants in the pre-Flood world, but ‘giant’ is a relative term. To some people groups today, a US basketball ‘dream team’ would certainly qualify for that description. But there are limits to the degree to which one can speculate about the size of past members of the human race, and it is likely that the approximately 2.7-metre (9-foot) Goliath was at or very near the size limit.
Say a giant was scaled 4 times the size of an average man. The mass would have increased 64 times, the cross sectional area of the leg bones would have only increased 16 times. So, in order to support the weight, the leg bone thickness would have to be increased dramatically. Many other aspects of this ‘scaling up’ issue would mean that the entire human body would have to have been totally ‘redesigned’, such that the person would look very, very strange indeed to our eyes, and not just because of the ‘giant’ aspect. http://creation.com/giant-footprint