How to measure the size of latch you need for your door.
Measure from the centre of the door handle to the edge of the door.
If this measurement is 44mm you would choose the 63mm (2.5inch)
latch
If this measurement is 57mm you would choose the 76mm (3 inch)
latch.
If these are to go on new doors you will want to measure from where
you will be putting your door handle so that it is centred on the panel.