I googled exactly what I suggested you use as a query, and (with a few exceptions), it all says the same thing. 5-5.25", 5.25 for Jeep alloys, 5.25 for all 7" wide wheels, and so on. Same with center bore.
FWIW, my buddy has 15x8 wheels with 3.5" of backspacing, and they stick out further than stock, so I know I can ignore any post where some kid claims stock wheels were less than 4" of backspacing.
You could also measure your spare.