Magnum? Large? Well, this matter requires further investigation.
Careful. The foil was torn, and some sidewalk detritus was inside. The things I do for science!
About two inches wide at the bottom, unstretched. So far, we have a big ho hum going here, and I detect marketing hype before me.
So let's unfurl the beast.
About eight inches, again unstretched. More hype, to be sure, though larger than what the population stats would suggest.
Sadly, there's no spiquot nearby, or we'd see what kind of water balloon is possible.