Size of Header Tiled Image to come out even on right

[Rev. O.M. Bastet]

I have FINALLY figured out what "Tiled Image" means and does!!!!

Let's ignore the fact that to get an image on the sides, you put it in as"Header Image," as -- at least in the old "Silver" template I am using, NOTHING shows up when I put it in the "Side Image" section.

Anyway, so to put an image, let's say a smallish image, into the Header, what is the pixel width which will allow it to show completely in the left-hand column, and also completely, in the right-hand column, of that template??? In other words, for the tiling effect to come out even across the page? I suspect it is approximately 150 pixels......

 

I know this is an awfully specific question, but we love to re-do our decor for holidays, and this issue is driving me bananas, trying to find images that work!!!