Vacuum forming a PETG dome.

Hello,

I first apologize for my writing, if there are mistakes, I am a French student.

I would like, as my title announced, to "vacuum form" a dome using a PETG.
But here's my problem : what would the dimensions of the PETG be, for a 27cm diameter, 41cm height, cylindric dome ?

I don't know if a 50cm x 60cm PETG can work, or if the plastic will tear itself apart given the fact it's too small. I would like the cheapest and smallest PETG I need, but also the most effective.
Does the thickness of the plastic count ? Will it change a lot if my PETG is 3mm thick rather than 1.5mm ?

I know it's more a mathematic problem, but, you guys surely have experience in vacuum forming, that's why I came to this forum, because real experience sometimes is worth more than scientific theories...

I also send you the exact dimensions of the dome I would like to create. Don't bother about its final thickness, any advice being welcome though.

Thank you for your understanding and your help.

Comrodd