The Rosenthal Collection Plastic Ring Mandrel and Sizer exclusively sold by Five Star Savings, is awesome for determining the size of a ring or your finger. for whatever your need it works great.
Plastic Graduated Ring Mandrel Used in Jewelry to measure ring sizes
Plastic Mandrel Measures up to Size 15, Handy Jewelers Tool
Plastic Ring Sizer Measures up to Size 13, Relaible Jewelry Finger Sizing Tool
Lightweight Jewelry Tool Set
Durable Jewelers Tool Set