How to Measure for Eyeglass Frames

Until recently, the general public did not need to know how to measure for eyeglasses: we simply went to the eye doctor, had our eyes examined, and then picked out frames at the doctor’s office with the help of an optical technician. Purchasing eyeglasses online is gaining popularity, however, as consumers discover they can reap significant savings. With a prescription in hand, the only other information you will need to order eyeglasses online are a few measurements to help you find a frame that will fit properly.


1 Get an eye exam first — this is essential. Not only will the eye doctor determine the prescription for your lenses, but he or she will also evaluate the overall health of your eyes. It is recommended that everyone get an eye exam at least every two years. The doctor will perform several tests, including checking for light reflection from the eyes, examining how an image focuses on the patient’s retina, and checking for amblyopia (otherwise known as ‘lazy eye’) and depth perception. The patient will also be screened for diseases of the eye, such as cataracts and macular degeneration.

2 Take the measurement of the distance between your pupils. Your doctor will perform this when he writes the prescription. This measurement ensures the optical centers of the lenses will be positioned directly in front of your pupils. If it is incorrect, eyestrain and headaches may occur. The measurement is abbreviated on your prescription as PD, and is measured in mm. You must know this measurement.

3 Look for numbers on your current eyeglass frames, which you will find either behind the bridge (nose piece) or on the inside of the arm piece. You must have these numbers when ordering frames online. An example of what you are looking for is: 47 22 140. The numbers are sometimes separated by a box shape. The first number represents “eye size.” The second number represents “bridge size.” The third number represents ‘temple/arm length.’ Enter these numbers in the appropriate places on the form when making your order.

Tips & Warnings
If you do not currently wear eyeglasses, it may be best to have your eye doctor’s optical technician assist you the first time you purchase a pair of frames.

Do not try to determine your PD on your own with a ruler. A doctor, using the appropriate tools needed for precision, must take this measurement.