Why does God give specific dimensions to build Noah's ark?

Answer 1

Probably because Noah had to fit 2 of each of the animals in the ark, and if the ark was too big then it might have took too long to build, or maybe if it was too big it would become too heavy, or so; and not too small or else the animals would not fit. In my opinion, I think the dimensions were not big enough to fit 2 of every single animal ever created because I think dinosaurs became extinct because Noah did not take them on the Ark. But, of course, that is just my belief. The dimensions might have also been so specific because God wanted to test Noah if he would do as God told him.

Answer 2

The biblical story of Noah's Ark actually has two, slightly different stories woven together to appear to be one complex and slightly confusing story. The first of these was written by the Yahwist source, who lived around 800-900 BCE, while the second story was written by the Priestly source, who probably lived during the sixth century BCE*. The Priestly source was often characterised by an obsession with the minutiae of measurements and counts, as in this case.

Footnote

* The verses attributed to the Yahwist are: Genesis 6:5-8, 7:1-5, 7:7, 7:10, 7:12, 7:16b-17, 7:22-23, 8:2b-3a, 8:6, 8:8-12, 8:13b, 8:20-22. The verses attributed to the Priestly author are: Genesis 6:9-22, 7:6, 7:8-9, 7:11, 7:13-16a, 7:18-21, 7:24, 8:1-2a, 8:3b-5, 8:7, 8:13a, 8:14-19, 9:1-17.