It depends on the company and the fabric line. Jelly Rolls from Moda typically have 40 strips. Often there are 38 fabrics in a line so they repeat a few. Hoffman Bali Pops have 40 different fabrics. Timeless Treasures Treat Strips have 40 strips, 2 each of 20 different fabrics.
I think you could cut your own however you like!
Andi