There is unfortunately not one standardised ring sizing system in the world. To make things easier when choosing the size of your ring. Please refer to the information below, showing the sizing and the internal diameter (across) of the ring based on the sizing we use here at Spindrift Collections. If you have a ring that is the right size, you can measure the internal diameter.

Size J -   15.40 mm Internal Diameter 
Size K -  15.80 mm Internal Diameter
Size L -  16.20 mm Internal Diameter
Size M - 16.60 mm Internal Diameter
Size N - 16.99 mm Internal Diameter
Size O - 17.19 mm Internal Diameter
Size P - 17.59 mm Internal Diameter
Size Q - 17.99 mm Internal Diameter
Size R - 18.39 mm Internal Diameter
Size S - 18.78 mm Internal Diameter
Size T - 19.98 mm Internal Diameter