How does "beyond a reasonable doubt" translate into a probability?

Suppose that at a crime scene, the proper procedures are followed for gathering evidence and a DNA analysis of blood samples shows there is a one in a million chance that they come from someone other than the defendant in a trial. Does one in a million count as being beyond reasonable doubt? It would seem to. What if the probability of match was 90%? That at first seems to be pretty good, but 90% chance of match means a one in ten chance that someone chosen at random would be a match. Surely that counts as reasonable doubt. Where is the dividing line between reasonable doubt and beyond reasonable doubt?