Understanding how to measure your pupillary distance (PD) is crucial for ensuring the proper alignment of prescription lenses in your eyeglass frames. While opticians typically measure PD during eye exams, you can also measure it at home using various methods, including digital tools like our PD ruler. In this guide, we'll explore the importance of PD measurement and provide step-by-step instructions for accurate measurement. 

What is Pupillary Distance (PD)?

Pupillary distance (PD) is the distance between the centers of your pupils and is essential for aligning prescription lenses accurately in your eyeglass frames. Every set of prescription lenses has an optical center that should align precisely with where you look through the lens. Thus, an accurate PD measurement ensures optimal visual clarity and comfort when wearing corrective eyewear. 

Why is it Important?

The optical center of prescription lenses must align with the center of your pupils to provide clear and comfortable vision. An incorrect PD measurement can lead to eyestrain, headaches, and discomfort. Therefore, it's essential to have an accurate PD measurement to ensure that your prescription eyewear functions effectively. 

Single and Dual PD: 

  • Single Pupillary Distance (Binocular PD): This measures the distance between the centers of both pupils. The average adult PD ranges from 54 to 74mm, while the range for children is typically between 43 and 58mm.
  • Dual Pupillary Distance (Monocular PD): Dual PD consists of two numbers, representing the distance between each pupil and the bridge of the nose. It is usually written as two numbers, such as 32/30, with the first number indicating the right eye (OD) and the second number indicating the left eye (OS).

Tools Needed for Measuring PD:

To measure your PD, you'll need: 

Step-by-Step Guide to Measuring PD: 

1.Using a Ruler

  • Stand in front of a mirror with your face straight and your eyes level.
  • Hold the ruler against your brow line, ensuring it's parallel to the floor.
  • Have a friend or family member measure the distance between the centers of your pupils in millimeters. Make sure they measure from the center of one pupil to the center of the other.
  • Repeat the process a couple of times to ensure accuracy.

2.Using a Mirror: 

  • Hold the ruler against your brow line while looking directly into a mirror.
  • Align the ruler horizontally with the zero mark at the center of one pupil.
  • Without moving your head, note the measurement where the center of the other pupil aligns with the ruler.
  • Repeat the process a few times to ensure consistency.

3.Using an Online PD Measurement Tool: 

  • Some websites offer virtual PD measurement tools where you upload a selfie, and the tool calculates your PD.
  • Follow the instructions provided by the website, usually involving uploading a photo and marking the centers of your pupils.
  • Be sure to use a reliable and accurate website for this method.

Tips for Accurate Measurement: 

  • Ensure proper lighting when measuring your PD to avoid inaccuracies.
  • Keep your head straight and level throughout the measurement process.
  • If you wear glasses, remove them before taking the measurement.
  • Double-check your measurements for accuracy and consistency.

Common Mistakes to Avoid: 

  • Tilting your head or looking away from the mirror while measuring can lead to inaccurate results.
  • Holding the ruler at an angle instead of parallel to the floor can skew the measurement.
  • Allowing the ruler to slip or move during the measurement process can result in errors.

What to Do with Your PD Measurement:

Once you have your PD measurement, be sure to provide it to your eyewear provider when purchasing new glasses or contact lenses. Your PD measurement ensures that your lenses will be correctly positioned for optimal vision and comfort. 


Measuring your pupillary distance may seem daunting at first, but with the right tools and techniques, it's a straightforward process that you can easily do at home. By taking the time to measure your PD accurately, you'll ensure that your prescription eyewear fits perfectly and provides you with the clear vision you need.

March 27, 2024 — Glasseslakoh