The best frame size can be determined by the following methods: A is the most important parameter to determine the size of the frame - the temple distance. Find a pair of glasses that are comfortable to wear and measure the temple distance between the frames. Refer to the table below to select the nearest size to determine the size of the frames. Frame size: small medium to large A -- Temple distance 126 mm 131 mm 139 mm B-lens diameter 50 mm 52 mm 56 mm C-mirror bridge width 15 mm 15 mm 15 mm Full-size frame: D -- Adjustable pupil distance -- Galilean type: 46mm-70mm D -- Adjustable pupil distance -- Prismatic type: 48mm-80mm