Round Swarovski Rivolis are measured by their diameter, e.g. 12mm, 14mm, 16mm, etc.
Peyote Stitch - Bead Bezel a Swarovski RivoliRule of thumb Formula
(Diameter x 2 ) + 4 size 11/0 seed beads.
12mm round rivoli - (12 x 2) + 4 = 28 seed beads
16mm round rivoli - (16 x 2) + 4 = 36 seed beads
Note: You will want to have even number of seed beads. This should give you the first round of beads around the rivoli.
RAW - Bead Bezel a Swarovski RivoliFor wanted of more proper terminology, I designate the below photo as 2 'squares'. When you join into a circle, then you will have 3 'squares'. That is one way of counting.
Alternatively, you can count the center (blue) beads - for 3 'squares', there will be 3 center blues.
Rule of thumb Formula
(Diameter + 2 ) 'squares' (or center beads)
12mm round rivoli - (12 + 2) = 14 center beads
16mm round rivoli - (16 + 2) = 18 center beads
Tip: This Right Angle Weave tutorial is a good place to learn how to RAW.