Regarding screen printing, common screen sizes can range from 13″ X 15″ to 30″ X 40″. You can also get them custom made to a size you desire, and your equipment can handle. However, my experience says that the most popular screen size for printing is 20″ X 24″.
A jumbo or oversized print can cover the majority of the body of a shirt which can easily extend to 16″ X 20″, while an all-over print can cover a garment’s full length, width, and sleeves.
All in all, a 20″ X 24″ screen can handle a large majority of your print sizes from standard to oversized/jumbo, and a larger screen is needed for an all-over print.