Measure the lens width
Measure the bridge width
Measure the temple arm length
Measure the lens height
Measure the frame width
Check the size markings on the inside of the temple arm
Use a ruler or millimeter measuring tool
Measure from hinge to hinge for frame width
Measure the widest part of one lens for lens width
Measure the vertical height of one lens for lens height
Measure the distance between the two lenses for bridge width
Measure from the hinge to the end of the temple arm for temple length