95mm external diameter.
The "blue" Fiat logo in the badge is 70mm.
Just a word of warning (if you want to call it that)....
The original badge is attached to the bodywork by double sided tape and by 2x push in connector lugs. Your new badge must either have lugs in the same place, or must (in some way) make provision to close the holes in the bodywork.
Another thing to look out for: the badge is fitted in a recess, but because of the way the bodywork is constructed, the underside of the badge is concave. Any new badge cannot be "flat"
I suggest that you prise the badge off and then get your calculations right..... I should have done that. Instead I ended up spending a crapload of time trying to make my new badge fit. Got it right eventually, but wasted a LOT of time