Maybe someone will know if this is true or urban legend. It seems plausible.
Today, the most common size for distilled spirits bottles is 750 ml. This is also the size of the typical wine bottle.
Prior to the adoption of the metric system for alcoholic beverages in 1979, the most common size for spirits was the "Fifth," which is one-fifth of a gallon. I believe wine bottles, too, were that size then.
I always wondered why. It's such an odd size. It isn't even an even number of ounces (25.6).
The size for whiskey bottles, it seems clear, evolved from the much old size for wine bottles but again, why?
I read or heard recently that it goes back to Roman times and was standardized as the volume of wine one man would normally consume in the course of one meal.