there are hundreds of standards and tolerances,agma,bs,iso and din just to name a few, each standard has classes and each class has tolerances within that class, i know this won't help you a lot but it will show you how there is no sraight answer to your question
The size over pins is calculated from the known tooth thickness (and another gear data). The tooth thickness is selected/calculated for desired backlash. Backlash can be taken from standards for desired gear precision grade or simply used as a known value which works OK for the gear's application.
Do not forget that tooth thickness has also tolerance, which depends on the precision grade...
As lbmakem mentioned - no simple answer to your question.
Just want to add that AGMA classes give fluctuating ranges for the variation on the tooth profile such as the total composite error and tooth to tooth error etc. But all these tolerances (except the reduction from tooth thickness and the tolerance on tooth thickness) are AC (alternating)values with analogy to electricity. The DC value is measured by the testing radius of the gear when meshed with a master gear or the dimension over pins. There are no standard values for the DC part of the gear dimension.
Dudley's gear handbook suggests backlash typically for general machine practice. Genrally it boils down to .015/dp to .040/dp. But if you need really quiet gears your backlash needs to be less than above values. As I said if you are designing gears for normal practice above values will work good.
