Use a ring you already wear on the same finger
Place the ring on a ring sizer chart (printable or in-store)
Measure the ring’s inner diameter in millimeters with calipers or a ruler
Convert diameter to ring size using a ring size conversion chart
Measure your finger circumference with a soft tape measure
Record the circumference in millimeters
Convert circumference to ring size using a ring size conversion chart
Measure at the end of the day when fingers are slightly larger
Measure 2–3 times for accuracy
If between sizes, choose the size that matches how the ring should fit (snug vs. loose)