Krakow is the second or third most populous city in Poland. However, the population of the whole metropolitan area is ca 1.3 Million. [1] or 1.7 Million [2]
At the larger estimate, that's about as big as Oxford or Slough, smaller than Swindon. At the smaller, High Wycombe or Grimsby [3], none of which would appear on a list of Big British Cities.
It's about 38 in the list of EU Larger Urban Zones [4]. Seven German cities appear higher in that list.
Wikipedia says even the Oxford metro area is only 244,000 people vs about 700k people for Krakow city alone.