What is the maximum width for 5/8 drywall that I can hang on the wall without a stud behind it?

How wide of a rip of drywall 5/8 can I put on a wall with out a stud behind it

16" to 24" depending on direction and application of adhesive vs no adhesive.

I would frame all my studs at a minimum of 18" on center for new walls and hanging drywall.

16 is typical 24 is allowed in some cases.

24" (610 mm) is the maximum stud spacing for 5/8" single-layer gypsum board per Gypsum Association specifications. Boards may be parallel or perpendicular to studs.

24"on center is generally the max spacing of studs