If you're in the market for a new pair of specs, chances are you've come across the term pupillary distance. This guide is a resource to teach you what pupillary distance is, and how you can measure it from the comfort of your own home. Your PD is easier than ever to measure, so your perfect pair of prescription glasses are just a quick read away.


What is Pupillary Distance?

Pupillary distance is the distance between the center of each pupil. It's also referred to as:

    • Pupil distance
    • Interpupillary distance
    • PD
    • IPD

Your PD will change depending on whether you're focusing on something near your face, or far away, and whether it is day or night. It can vary considerably from person to person, so you always need to measure your PD individually rather than generalizing based off of your age and gender.

Why Do We Measure Pupillary Distance?

It's vital to know your pupillary distance when you're purchasing eyewear because the optical center of each lens must be directly centered with each pupil. Failure to provide an accurate PD measurement can cause eye strain, blurriness, or double vision. This is especially important when you're being fitted with progressive, or multifocal, lenses. The more precise your measurement, the more effective your prescription will be.

How Do You Measure Pupillary Distance?

Opticians use a pupillometer to measure your PD, but it's simple to do at home with a ruler as well. You will use millimeters to measure your pupillary distance.

  1. Either ask someone to assist you or stand about 8 inches away from a mirror.
  2. Hold the ruler horizontally directly over your right pupil. Place against your brow for added stability.
  3. Look straight ahead and measure the distance in millimeters between the centers of your right and left pupils.
  4. Repeat this process a few times for a more accurate final measurement.
  5. Enjoy comfortable, clear vision when your prescription arrives!


In addition to the ruler method, there are several apps you can download that detect your pupils when you take a photo of yourself. These apps can calculate your PD for you as long as you have a camera phone and a card with a magnetic strip.