Measure the lens width: the horizontal width of one lens at its widest point, in millimeters
Measure the bridge width: the distance between the two lenses at the narrowest point, in millimeters
Measure the temple arm length: from the hinge to the end of the arm, in millimeters
Measure the lens height: the vertical height of one lens at its tallest point, in millimeters
Measure the frame width: the total width of the frame from outer edge to outer edge, in millimeters
Measure the bridge fit: check how the nose bridge sits across the nose
Measure the pupil position: compare lens center placement to your pupils
Check the frame size numbers printed on the inside of the temple arm
Compare measurements to a pair of glasses that already fits well
Use a ruler or millimeter caliper for accurate measurements