The rotational correlation times of individual asphaltene molecules have been determined using fluorescence depolarization techniques, addressing an active, long-standing controversy. Using simple theoretical models and using model-independent comparisons with known chromophores, a range of asphaltene molecular diameters is obtained of 10-20 Angstrom. Comparison with corresponding data of known chromophores indicates a molecular mass for asphaltene molecules of 500-1000 amu. Furthermore, we have performed the first direct measurement correlating molecular size with constituent chromophore size; we establish that the bulk of asphaltene molecules possess 1 or 2 (aromatic) chromophores per molecule. Similar results are found for the largest aromatic molecules of the de-asphaltened crude oil.