Ohiotom, 

P/E is based on earnings, not gross revenue. So if we've got $3 billion in gross revenue (sales), a multiple might be 4, or $12 billion of market cap. 

Of course, our earnings would likely be quite large with such revevue, maybe $1.5 to $2 billion. I'd assign a 25 P/E to that, so $37.5 to $50 billion market cap. 

I would consider the above hyperbolic!