The modern Kuiper belt is the remnant of a much more populous primordial belt that was dynamically sculpted during the solar system’s era of giant planet migration. As such, the primordial Kuiper belt must have contained many more ~Pluto-mass bodies than the two such bodies found in the modern belt (Pluto and Eris). Using the GPU-accelerated N-body code GENGA to model the full gravitation of the population of Pluto-mass bodies, we simulate the dispersal of the primordial belt with varying numbers of Pluto-mass bodies. Our work indicates that the number of Pluto-mass bodies affects how quickly planetary migration initiates, the speed at which it proceeds, and the rate that the primordial Kuiper belt’s mass is depleted. We conclude that the primordial Kuiper belt possessed fewer than ~1000 Pluto-mass bodies and perhaps as few as 200.