Given that a human body contains about 3-5 grams of iron total, those teeth must be smaller than they look.

My extremely rough math suggests 282-470 people go into the making of those teeth, assuming xenomorph teeth are roughly 10x the volume of a human tooth (5-6 mL) and that they have thirty of them, no losses, and we're talking pure elemental iron and not a protein/metal matrix or otherwise. Figure 7.8 g/mL as the density of iron, by 6 mL per tooth is roughly 47g per tooth, so in the ballpark of 10-15 humans worth of iron per tooth. Humans have 32 teeth and 30 seems as good as any other number, so 47g/tooth by 30 teeth is 1410g of iron. That gives us somewhere between 282-470 people per set of xenomorph teeth.

I don't know where exactly I was going with this but it was fun to estimate.

They just eat tons and tons of people.

It’s almost as if the Aliens story universe is fictional, bruh.