Ahh, now here comes the fun part. There is no standard.
250ml is 8.5 ounces. Some places in Europe standardized on this.
A cup of anything else is 8 ounces.
A "cup of coffee" (the actual unit) is 6 ounces, and this is the standard everywhere where 250ml isn't, and we're not in Japan; but even though the US follows the 6 ounce standard, the USDA considers a cup 8 ounces on their nutrition table.
Japan has standardized on 200ml (or about 6.7 oz).
What SHOULD be measured is not liquid volume, but bean weight (measured in grams; even Ameicans measure it in grams when they're the type to weigh it instead of just throwing ambiguously heaped tablespoons in); and then shifted according to that blend's particular caffeine content (outside of specialty products with high-caffeine bean variants, caffeine content can vary about +/- 50% depending on the origin of the beans (roasting does not effect caffeine content meaningfully, although the myth lives on)).
250ml is 8.5 ounces. Some places in Europe standardized on this.
A cup of anything else is 8 ounces.
A "cup of coffee" (the actual unit) is 6 ounces, and this is the standard everywhere where 250ml isn't, and we're not in Japan; but even though the US follows the 6 ounce standard, the USDA considers a cup 8 ounces on their nutrition table.
Japan has standardized on 200ml (or about 6.7 oz).
What SHOULD be measured is not liquid volume, but bean weight (measured in grams; even Ameicans measure it in grams when they're the type to weigh it instead of just throwing ambiguously heaped tablespoons in); and then shifted according to that blend's particular caffeine content (outside of specialty products with high-caffeine bean variants, caffeine content can vary about +/- 50% depending on the origin of the beans (roasting does not effect caffeine content meaningfully, although the myth lives on)).