What size rose should I use?

The rose (or rosette) is the round metal plate that sits against your door behind the lever handle. 

Selecting the correct size is more straightforward than you may think:

Do you have new doors with no holes?

If so - you can use whichever size you like. Simple!

Do your doors have existing holes in them?

In this case - there are generally two size ranges to consider once you have confirmed what size holes are in your door:

25-45mm holes? Use a 52mm rose

50-54mm holes? Use a 63mm rose