Unit frontage?

[Ratzki]

I was wondering, during ww2, what would be the optimum frontage for an Infantry Battalion/Regiment/Division? I know that terrain plays a huge role in the equation, but there must be a certain troop density where the men are not tripping over one another or so spread out that they are ineffective. I was reading about a thrust into Stalingrad being on a 3km front and was just wondering what formations that size front would contain, which is where the question comes from. I am more looking for a loose rule of thumb(if such a thing exists) that i can apply in future readings.