What is the cord blood transplant dose?

In other words, how much cord blood is needed to be confident of a successful transplant?   The crucial thing is not the volume of the blood sample, but the number of stem cells it contains. The simplest measure of these cells is the Total Nucleated Cell count, or TNC.   

For treating cancer, the transplant dose should be at least 30 million nucleated cells (TNC) per kilogram of body weight (one kilogram equals 2.2 pounds). 
References:
Eapen et al., Lancet (2007) 369: 1947–54, and subsequent statistical analyses presented by CIBMTR (see slide).

But, how many TNC are there in the volume of cord blood collected?  The concentration of TNC per volume varies greatly from one collection to another, with smaller collections often having higher concentration.  The average concentration of cord blood is 8.6 million nucleated cells (TNC) per MilliLiter.
Reference:
W Reed, et al, Blood 2003; 101(1):351
This study averaged 542 families that banked cord blood through the Sibling Donor Cord Blood Program of Childen's Hospital of Oakland.  Those collections are representative of family banking, because the cord blood was collected by the family's personal OB/Gyn, at hundreds of different hospitals.  The average cord blood volume and nucleated cell count were 103.1 mL [including anticoagulant] and 890 million, respectively.

The optimal transplant dose is a subject of ongoing research.  The numbers presented here are based on studies of cord blood transplants, for malignancies, in which the donor was a 5/6 or 6/6 match to the patient.  There is an opinion in the transplant field, not yet proven, that TNC dose should be increased by 10 million TNC per kg for each degree of mis-match between donor and patient.  Also, these numbers only refer to transplants for blood cancers.  Transplants for hereditary blood disorders (ex: Fanconi Anemia, Sickle Cell) or metabolic disorders (ex: storage diseases) usually  have a higher cell dose per kg because they are performed on small children.