Use a ring sizer tool or printable ring size chart
Measure a ring you already wear on the same finger
Wrap a thin strip of paper or string around your finger
Mark where the ends meet
Measure the length with a ruler
Compare the measurement to a ring size chart
Measure your finger at the end of the day
Measure when your hands are warm
Measure the exact finger you plan to wear the ring on
Repeat the measurement a few times for accuracy
Visit a jeweler for a professional sizing