A magnetic field will induce a ferrofluid to form a magnetic dipole. This magnetic dipole of the ferrofluid will then experience force from the the magnetic field in proportion to the strength of the magnetic field multiplied by the strength of the induced dipole, times other constants dependent upon the orientation and curvature of the magnetic field and the nature of magnetism. The strength of the magnetic field of course depends on the strength of the magnet; the degree of magnetization of the ferrofluid will depend on how magnetic the fluid is. This will be in the form of a magnetic susceptibility constant, and will vary from one ferrofluid to another. I am certain that the Handbook of Chemistry and Physics contains such constants for a variety of ferrofluids, provided that the edition of the handbook is new enough. I do not know what the equations are for calculating the magnetic force on a magnetic dipole from an existing magnetic field, or how to derive the strength of a magnetic field from an existing magnetic dipole. They would probably be available in a high-enough level college physics text, but I don't remember ever being exposed to them in basic physics (and, being a biologist, that's all I went through).