It is 255.66 miles accoring to MapQuest assuming that the desired Calais is the city in Maine an not the Calais in France.
275 km taking this route: Take A16 BOULOGNE (partially tolled) from Calais to A28 to LE HAVRE at SORTIE (EXIT) 23. Take A28 to A29 (péage [toll]) to LE HAVRE. Take A29 to A131 to LE HAVRE. Take A131...
703.21 kilometres (436.96 miles)
339.01 kilometres (210.65 miles)
1,688.58 kilometres (1,049.24 miles)