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How To Measure Your Pupillary Distance (PD)

How To Measure Your Pupillary Distance


Are you ordering a pair of prescription glasses online? If so, it is important to measure your pupillary distance and this guide will explain how to do this without professional help.

Your pupillary distance - also known as PD - is the measured distance between the centers of your pupils. It is used to identify what point you will be focused on when looking through a pair of glasses. As such, it must be as accurate as possible.

The average PD for an adult is between 54 and 74 mm. For children, it is approximately between 43 and 58 mm.

It is possible that you do not have your PD from your optician. If this is the case and you are choosing to order glasses online, you will need to measure it yourself.



Why Is Your Pupillary Distance Important? 

Every pair of prescription lenses that you purchase has an “optical center.” This will always be determined by your unique individual pupillary distance and therefore it is essential for the purchase of any lenses.

You will also need your PD for the purchase of blue light prescription glasses. Blue light prescription glasses are used to reduce the blue light from computer screens and devices. This can have a significantly positive impact, reducing issues with:

  • Headaches
  • Dry eyes
  • Tired eyes
  • Blurred vision
  • Insomnia

These glasses are highly recommended for anyone who spends a significant period looking at a computer screen or similar device.



How To Measure Your Pupillary Distance

To measure your pupillary distance, you will need a mirror and a ruler. You should stand about 30 cm away from the mirror. Once you have done this, you can then look directly at the mirror image and hold the ruler against your eyebrows.

 Once you have done this, close your right eye. You can then line the ruler up so that the 0 mm mark is now directly above the middle of your left pupil.

 Now open your right eye and close your left. The PD measurement will be the figure you see that lines up at the center of your right pupil. You should find it falls somewhere between the averages mentioned above.



Is This The Process For All Glasses?

Reading glasses are slightly different. To measure your PD for reading glasses, you need to complete the same process. However, you should take 3 mm off the number. This will allow you to calculate the correct PD.



Measuring Another Person’s PD

You might need to help someone measure their PD. For instance, children will often need support to get the right number.

To do this, you should have them look at something that is roughly 20 feet away. Both of their eyes should be open. When they are focused on the object, line up the 0 mm mark for one pupil, and then measure the distance to the center of the other pupil.

It is important when completing the measurement to stay out of their line of sight. They should keep looking straight ahead and not focus on you when you are measuring the distance. To ensure that they avoid looking at you during this process, you can consider crouching or sitting. This will keep you out of their field of vision.

Typically, you will need to complete the process several times to make sure that you get a consistent number. It’s easy to understand if you are completing the process the right way.



What Is Dual PD?

Some prescriptions will require a dual PD. This is also referred to as monocular PD. Here, you will have two numbers. Each number will relate to the distance from the center of the pupil to the bridge of the nose. They are typically written in a format such as 30/32. The first number will always refer to the right eye and the second will refer to the left. It can be measured in the same way as the typical PD except you measure twice from reach pupil to the bridge.

If you are using dual PD for reading glasses, you need to ensure that you are subtracting 1.5 mm from each measurement. So, if your measurement is 32/30, then your PD would actually be 30.5/28.5.

We hope this helps you understand how to measure your PD the right way and why this is important. Remember, you can always book an appointment with an optician to receive the most accurate measurement.


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