Eye Size. Eye size is the horizontal width of the frameâs lens in millimeters. Usually, the eye size ranges from 40 mm to 60 mm. Bridge Size. Bridge size is the distance between the two lenses in millimeters and typically ranges from 14 mm to 24 mm. Temple (Arm) Length. Temple length is measured along the length of the temple from one end to the other and also includes the bend. Your temple length can fall between 120 mm and 150 mm. Lens Height (B) It is the vertical height of an eyeglasses lens which is measured from the tip to the bottom of the lens aperture of the frame. The B measurement is important for bi-focal lenses or progressive lenses.