Hi @MummaMia69, welcome to our forum!
In the White paper for the Xperia XZ you can find the follow information regarding the size of the display and the size of the device.
Size of the device: 146 x 72 x 8.1 mm.
Size of the display: 5.2 inches (diagonal).
Do note that you will need a case/cover that has been made especially for the Xperia XZ otherwise volume buttons/power button and so on will not be in the correct place and you will not be able to access these buttons.
I hope that helps! 
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