To measure the frames you would need a millimeter rule and your old pair of glasses. Please follow the steps below to measure your frame for correct size:
Measuring Lens Width
Lens width is the size of the lenses. Place the ruler near the nose bridge so that the zero is on top of inner rim of the frame as shown on the picture above.
Now take the reading from the inside of the other rim. When comparing the frame size with your frame, if there is a difference of 2-3 mm in lens width the size is acceptable.
Measuring Bridge Width
Bridge width is the size of the Bridge. Place the ruler on the nose bridge so that the zero is at the outside of the rim as shown in the picture above
Now take the reading of the other side of the nose bridge. When comparing the frame size with your frame, if there is a difference of 1-2 mm in lens width the size is acceptable.
Measuring Temple Arm
Now take the linear reading of the temple arm where the arm ends. When comparing the frame size with your frame, if there is a difference of 3-5 mm in temple arm the size is acceptable.
Measuring Lens Height
Lens Height is the height of the lenses. Place the ruler vertically so that the zero is on top of inner rim of the frame as shown on the picture above.
Now take the reading from the inside of the other side of rim. When comparing the frame size with your frame the difference on height of the lenses depends on how large frame you would prefer.
Measuring Total Width
Total width of the frame is from the temple arm to temple arm. Place the ruler at the inside of one temple so that the zero is placed at the inside of the temple arms shown on the picture above.
Now take the reading from the inside of the other side of temple. When comparing the frame size with your frame, if there is a difference 3-5 mm in Total Width the size is acceptable.