How much postage for a 6.5 X 6.5 envelope?

Well, darling, a 6.5 x 6.5 envelope falls under the square envelope category, which requires extra postage. So, you'll need to slap on a couple of extra stamps to ensure it reaches its destination without any postal drama. Just make sure you check with your local post office for the exact amount, because those rates can be as fickle as a cat on a hot tin roof.