The RTX 4090 measures 304mm (11.9 inches) by 137mm (5.3 inches) in width. Yes, it's that big. The RTX 4090 is also a three-slot card. That means it takes up what Nvidia says is 61mm (2.4 inches) of space - what you may call depth - in your case.
In terms of weight, and it will depend on the specific construction from partners, you're looking at over 2,000g. Yes, that's 2kg, or 4.4 pounds. In some cases - we're looking at you ASUS ROG Strix OC - the weight may be as much as 2,500g. That's 5.5 pounds!