When shopping for glasses online, one of the most important (but often overlooked) numbers you’ll need is your pupillary distance, or PD. This simple measurement can make a world of difference in how clearly you see and how comfortably your glasses fit. In this blog post, we’ll break down what PD is, why it matters, and how you can measure it yourself at home.
What Is Pupillary Distance (PD)?
Pupillary Distance is the distance between the centers of your pupils, measured in millimeters (mm). It’s used to determine where the optical center of your lenses should sit in your frames—this ensures that you're looking through the clearest part of the lens when your glasses are on.
If the PD is off, your lenses may feel “off” too—causing headaches, eye strain, or blurred vision, especially in high-prescription or multifocal lenses.
There are two main types of PD:
- Binocular PD – A single number that measures the total distance between your pupils (e.g., 63mm).
- Monocular PD – Two separate numbers that measure the distance from the bridge of your nose to each pupil (e.g., 31.5mm / 31.5mm). This is more precise and typically used for multifocal or progressive lenses.
Why Is PD Important?
Imagine trying to look through binoculars that aren’t aligned with your eyes. It wouldn’t feel right, would it? That’s essentially what happens when your PD is off in your glasses. PD ensures your lenses are centered to your vision, not just the frames.
Whether you're ordering single vision lenses or progressives, a correct PD ensures:
- Proper lens alignment
- Accurate prescription performance
- Less eye fatigue
- Better focus and visual clarity
Can I Find My PD on My Prescription?
Sometimes—but not always. Eye doctors don’t always include PD on your prescription unless you specifically ask for it. If your optometrist didn’t provide it, or if you lost your old pair of glasses, don’t worry—you can still measure it yourself.
How to Measure PD at Home (With Help or Solo)
You don’t need fancy equipment to measure your PD. Here’s how to do it with a ruler and mirror, or with a friend.
Option 1: With a Friend
This is the easiest and most accurate DIY method.
You’ll Need:
- A millimeter ruler
- A pen and paper
- Good lighting
Steps:
- Sit down facing your friend at eye level.
- Have them hold the ruler across your brow, resting it just above your eyes.
- Ask them to close their right eye while you look straight ahead.
- Have them align the zero mark of the ruler with the center of your left pupil.
- Then, they close their left eye and open the right, and measure the distance to the center of your right pupil.
- That number (in mm) is your PD!
Option 2: By Yourself (Using a Mirror)
If you’re flying solo, this method works great too.
You’ll Need:
- A millimeter ruler
- A mirror
- A steady hand
Steps:
- Stand about 8 inches (20 cm) from a well-lit mirror.
- Hold the ruler against your brow, directly over your eyes.
- Close your right eye and look straight into the mirror with your left eye.
- Align the zero of the ruler with the center of your left pupil.
- Now close your left eye and open your right.
- Without moving the ruler, read the number aligned with the center of your right pupil.
- That’s your PD!
Bonus Option: Use a PD App
There are several apps available that can help you measure your PD using your phone’s camera. Just follow the app’s instructions and it’ll give you a digital PD reading. Look for reputable apps with good reviews and be sure to check if it’s approved by eyewear retailers.
Tips for Best Accuracy
- Take the measurement 2-3 times to ensure consistency.
- Keep your head and ruler still while measuring.
- Use a digital ruler or print a PD ruler template for better precision.
- If your eyes aren’t symmetrical, consider measuring monocular PD (left and right separately).
What’s a Normal PD Range?
For most adults, PD ranges between 54mm and 74mm. Children usually fall between 43mm and 58mm. If your measurement lands outside that, it’s worth double-checking your results—or asking a professional.
Here’s a quick reference:
| Age Group | Average PD Range |
|---|---|
| Children | 43mm – 58mm |
| Adults | 54mm – 74mm |
Final Thoughts
Measuring your PD might sound technical, but it’s surprisingly simple once you get the hang of it. With just a ruler and a mirror—or a little help from a friend—you can confidently order glasses online that are customized for your eyes.
Don’t let PD hold you back from getting stylish, high-quality glasses at a great price. Taking five minutes to measure your pupillary distance could save you days of discomfort and ensure your vision is spot-on.