How do I control height and width of shapes made with pen tool?

Hi! I assume this is gonna end up being a rhetorical question, but how do I make shapes with the pen tool that are of an EXACT HEIGHT AND WIDTH? It doesn't look like there's an easy/obvious way of doing this, which I find appalling. Of course, this is where someone derisively asks "why's that such a big deal?" Why wouldn't this be an option?