Http overhead

Hi!

I am currently working with a traffic model for an IP network. I have a
question about the amount of overhead involved when transfering binary
files over http. As fas as I understood, http handles binary files so no
encoding has to be performed (as for example files over SMTP uses MIME).
So, how many header-bytes does http add in each packet when sending a
binary file from a server to a client?

I hope someone can help me with this.

Thanks,
Patrik