So I am designing a to go menu in InDesign and am trying to figure out the correct measurement.

Its an awkward paper size, but its based off the measurements of the old one, anyway it has a tri-fold with each page being 5.25 wide and 8.5 tall(Client says its a book size, ill admit that I am a newb). I want everything to center correctly so I divide 5.25/2 and come up with 2.6. Pretty Basic right? So what does 2.6 = to in actuall inches terms? I try to make a fraction with 2.6 and get 2 3/5ths.

Really want to know where to place my guide!

Thanks in advance!