You Can Measure Your PD at Home, but Should You?

Pupillary distance refers to, well, the distance between your pupils. It seems simple enough, but it’s best measured by an optician. Here’s why.

Man looking in the mirror

There are a lot of things you can do at home. You can learn a new language online. Bake a cake for your child’s birthday. Paint your nails. Refinish a piece of furniture. 

But just because you can do certain things from the comfort of home doesn’t necessarily mean that you should. And measuring your pupillary distance, or PD, is one of those things.  

PD measures the distance between the centers of each pupil. Sometimes, PD will also be taken from the pupil of each eye to the bridge of your nose. 

Having a pupillary distance measurement is important when ordering prescription eyeglasses because it ensures that the lenses are aligned with your eyes, so that you can focus properly and see crisply and clearly, says Natalie Martin, a Tampa, Florida–based optician and regional learning specialist for National Vision, Inc. 

If you choose to order eyeglasses online and manually enter your prescription information, you’ll be asked for your PD. But what if you don’t know this number? 

While it may be tempting to try to measure it yourself, here’s why you’re better off visiting your local America’s Best and leaving it to the professionals.  

Has it been a while since your last eye exam? Now’s the time to book an appointment!  

Can I Just Guess My Pupillary Distance? 

Short answer: no. Although the average PD for an adult is 63 millimeters (mm), getting it wrong means that you will end up looking through the wrong part of the lens. This could lead to eyestrain or wavy or blurry vision, says Martin. 

What Are Some Ways People Try to Measure Their PD at Home? 

There are a surprising number of ways people try to measure their own PD, including: 

  • Using a ruler and mirror 
  • Using a special pupillary distance ruler purchased online 
  • Using your glasses and a ruler 
  • Using an app or online programs 

For example, one popular method is to use a ruler and a mirror. You’d line up the edge of the ruler with the center of one pupil and measure the distance to the center of your other pupil. However, it’s easy to introduce an error, even if you do it carefully.  

“It’s difficult to be able to focus and look straight ahead while looking at the ruler in a mirror,” says Martin. “Your eyes converge in different ways depending on where you’re looking.” 

Why Is It a Bad Idea to Measure Your PD at Home? 

The DIY route saves you a trip to the eye doctor, and online articles and videos make it sound foolproof. The truth is anything but, says Martin. “Taking your pupillary distance measurement at home or with an app is possible, but will it be accurate? Probably not,” she says. 

Research suggests that there is a lot of human error when you do it at home. An older study concluded that self-measuring (or measuring a friend’s) PD was of “poor accuracy” compared to having a trained professional do it. More recent research analyzing smartphone apps found that they are off by 0.5 mm to 1.4 mm. 

“We take our job seriously. If a measurement is not accurate, we can fix it. But if you take a PD on your own and use that information to order glasses and it’s wrong, we have fewer options to help you,” says Martin. 

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So, How Should I Get My PD Measured? 

Having a trained person taking your PD is best. During an eye exam, your optician will most likely use a special device called a pupilometer, which will provide the most accurate PD measurement. Sometimes you won’t see your PD on an eyeglasses prescription. If that’s the case, you can simply ask your optician for this information, which will come in handy if you’re ordering glasses online. 

“We recommend seeing your optician,” says Martin. “It’s too easy to do this wrong, and if that happens, it can impact your vision.” 

Opticians have the right tools and expertise, so you can be confident that you end up with the right PD measurement. 

See our sources: 
Pupillary distance: Cleveland Clinic 
Accuracy of self-measuring PD: Optometry and Vision Science 
Effectiveness of smartphone apps for measuring PD: Cureus