Noah’s Ark and the each pair of animals

QUESTION: The Bible says Jehovah destroyed the world with the flood and that Noah and his family were commanded by Him to build an ark. God also told him to bring a pair of animals. If that Ark is the size of football field (so as to speak), how many pairs of animals does it hold? Yes, only the land animals in that ark, and also for argument sake we can tell that all the birds were on rooftops. Is there an explanation? I know Bible is God's word, but I am eager to know how?