There is no constant ratio between average marrow cellularity as measured by number of total nucleated cells per mL and the number of Colony-forming unit fibroblast (CFU-f). Hernigou et al in several authoritative studies linked clinical outcomes in non-union and osteonecrosis to the number of CFU-f cells in the graft.  Controlling for volume, Hernigou noted that 70% of the variation in CFU-f from patient to patient was due to variations in the quality of the marrow aspirate or idiosyncratic to the patient with the remaining variation being due to the number of nucleated cells per mL in the aspirate. Statistically, the only variable Hernigou reported to be significant was CFU-f and not nucleated cells per mL. Interestingly, CFU-f is found frequently in marrow and very rarely in peripheral blood.
Therefore, it seems reasonable to suggest that a graft needs to contain greater than 1000 progenitors/cm³
Hernigou P, et al. Treatment of Osteonecrosis with autologous bone marrow grafting. Clinical Orthopaedics and Related Research. 405:14-23, 2002.
Hernigou P, et al. Percutaneous Autologous Bone-Marrow Grafting for Nonunions – Influence of the Number and Concentration of Progenitor Cells. J Bone Joint Surg Am. 2005 Jul;87(7):1430-7.