Place the ring on the mandrel at the point where it fits snugly
Read the size marking at the top edge of the ring
Use the inner edge of the ring as the reference point
Check whether the mandrel uses US, UK, or metric sizing
If the ring sits between two marks, use the larger size for a tighter fit or note the half size if available
Measure multiple times to confirm accuracy
Make sure the ring is level and not tilted on the mandrel
Use the smallest point where the ring can pass comfortably if the ring is tapered
Read the engraved numbers or letters on the mandrel directly
Convert the reading to the correct sizing system if needed