Use a ring you already own that fits comfortably
Place the ring on a ring-sizing chart and match the inside diameter or circumference
Measure the inside diameter with calipers if available
Measure the inside circumference by wrapping a strip of paper or string around the inside of the ring, marking where it overlaps, then measuring the mark length with a ruler
Record the diameter (mm) or circumference (mm) and convert using the chart for your region’s sizing system
If measuring your finger directly, wrap a flexible measuring tape around the finger at the knuckle and at the spot where the ring will sit
Record the circumference in mm
Convert the finger circumference to ring size using a conversion chart
If using paper/string for your finger, wrap snugly (not tight), mark overlap, then measure the length in mm
Measure at the time of day when your fingers are typically at their average size
Measure both hands and compare results if sizes vary
Measure twice for confirmation
Consider that rings may need adjustment for comfort if you prefer a looser or tighter fit