Just a heads-up, get more than one postage quote and go with the higher one.
I went four different times. I was told two forever stamps twice and three forever stamps twice. I went with the three to be safe because I've heard stories of them getting returned, people having to pay the excess shipping, etc.
I just wish the PO would all be on the same page. The two workers that told me three stamps said it's because they're square and oversized, but the two workers that told me two stamps said it fit within their regular measurements. So frustrating!