It depends of definition of "metropolitan area". 425,000 is the city proper, 605,000 is Bratislava region and about 1.15 million including surrounding Trnava region (what is a half of western Slovakia area). But note that all these data are based on the population living in Slovakia only. As you know, Bratislava directly borders Austria and Hungary.
Bratislava region, 2 053 km², population 606,753
Trnava region, 4 158 km², population 551,000
