Flux and current are distinct concepts in neutron calculations, with flux measured in neutrons per square centimeter per second and current in neutrons per second. Current is derived from the flux integrated over a surface, highlighting that flux is a scalar and current is a directional vector. To calculate the ratio of total neutron current to total neutron flux in MCNP, one must integrate the flux over the relevant surface area. The specific method of calculation will depend on the details of the problem at hand. Understanding these definitions and relationships is crucial for accurate neutron transport simulations.