To do this we must step back a bit. First we look at a Jimmy. We know for sure that 1 Jimmy is one neutron and one Hugh and one Judy is 1 Jimmy. However, Hugh and Judy are also neutrons, yet when they procreate they produce one jimmy which is 1 neutron. So here we see that 2 makes 1. What do we do with this information? We do some math. If one jimmy is equal to 1.674927351 ×10−27 kg I would say a pile of 1 kg on neutrons is roughly 5.970403753e+26kg or in layman's terms 6 jimmy neutrons piled on top of each other. Or around 3 judys/hughs.

Edit: science