How to Measure Your Pupillary Distance (PD)
How to Measure Your Pupillary Distance (PD)
If you've come across the term "PD" on your prescription or during checkout and weren't sure what it meant — you're not alone. Pupillary distance is a small but important detail that ensures your lenses are crafted precisely for your eyes.
What Is Pupillary Distance?
Pupillary distance (PD) is the measurement in millimeters between the centers of your two pupils. This number tells us exactly where to position the optical center of each lens, ensuring you see with the greatest possible clarity and comfort through your Ra Optics glasses.
Your eye doctor can measure your PD during an exam and may include it on your prescription. If it isn't listed, no need to worry — you can measure it yourself at home with a few simple steps.
Single PD vs. Dual PD
Single PD
Single PD measures the total distance between both pupils and is the most common format. It is also referred to as binocular PD.
Dual PD
Dual PD measures the distance from each pupil individually to the center of the nose bridge, resulting in two numbers — one for the right eye and one for the left (for example, 31/30). This is also called monocular PD and is particularly useful for progressive lenses.
Either format works for ordering most Ra Optics styles.
What's a Typical PD?
Most adults fall somewhere between 60–64 mm, though PD varies from person to person. There is no "correct" number — what matters is that your measurement is accurate for you.
How to Measure Your PD
Get an accurate reading in under a minute. Use your device's camera—no tools needed. Prefer doing it manually? A mirror or a friend will do the trick.
Method 01
On-Site Measurement Tool
- Tap the button below to launch the tool.
- Allow camera access when prompted. Works on any phone, tablet, or computer with a front-facing camera.
- Follow the on-screen guide. The whole process takes under a minute.
- Your PD will appear on screen. Enter it at checkout or save it for your prescription.
Method 02
Mirror and Ruler
- Stand approximately 8 inches from a mirror in good lighting.
- Hold a millimeter ruler flat against your brow line, looking straight ahead.
- Close your right eye and align the ruler's zero mark with the center of your left pupil.
- Open your right eye and close your left eye.
- Note the millimeter mark that lines up with the center of your right pupil. That number is your PD.
Method 03
Ruler and a Friend
- Look straight ahead and focus on a fixed point approximately 10–20 feet away. Keep your gaze still.
- Have your friend hold the ruler along your brow line, aligning the zero mark with the center of one pupil.
- Ask them to read the millimeter mark that aligns with the center of your other pupil. That is your PD.
A Note on Reading Glasses
If you are ordering readers, subtract 3 mm from your single PD to arrive at your near PD. For a dual PD, subtract 1.5 mm from each eye's number.
If your prescription includes a prism correction, we recommend having your PD measured directly by your eye doctor or optician for the most accurate result.
Questions? Our team is always here to help — don't hesitate to reach out.
