Reasonable doubt is not a quantifiable concept. It is an error in law to instruct a jury to consider it in the manner you describe.
Reasonable doubt is not amenable to mathematical calculation or even analogy to probability. It is a wholly different kind of threshold. Reasonable doubt is binary, not a matter of degree. It is an error for a judge to liken reasonable doubt to a degree of certainty; doing so warrants a new trial (R. v. Bisson,  1 S.C.R. 306).
This is not a probabilistic exercise. No matter what probability threshold one might set, there would be doubts greater than that threshold that would nonetheless not be reasonable doubts if they were not based in the evidence or lack of evidence. The quality and source of the doubt, not merely its magnitude, are critical to determining the reasonableness of the doubt.
The Supreme Court of Canada has explained (R. v. Lifchus,  3 S.C.R. 320):
the standard of proof beyond a reasonable doubt is inextricably intertwined with that principle fundamental to all criminal trials, the presumption of innocence;
the burden of proof rests on the prosecution throughout the trial and never shifts to the accused;
a reasonable doubt is not a doubt based upon sympathy or prejudice;
rather, it is based upon reason and common sense;
it is logically connected to the evidence or absence of evidence;
it does not involve proof to an absolute certainty; it is not proof beyond any doubt nor is it an imaginary or frivolous doubt; and
more is required than proof that the accused is probably guilty ‑‑ a jury which concludes only that the accused is probably guilty must acquit.