Pupillary Distance Measurement

What is a PD?

Pupillary Distance Measurement

The PD (Pupillary Distance) is a horizontal measurement from the center of the left pupil to the center of the right pupil, in millimeters. This measurement is needed to ensure that the wearer's pupils align with the Optical Center (OC) of each lens. The optical center of the lens has a small tolerance zone (around 1-2mm) where vision remains optically clear and accurate. 

The PD alignment to the lens optical center is essential for both clear vision and overall eye comfort. Without it, even a perfectly made prescription may not work as intended. This alignment is especially crucial with progressive lenses, where the near, intermediate, and distance zones must line up precisely with the line of sight.
 

• It's common to round up the PD to the nearest 0.5 mm, as this generally remains within tolerance of the lens optical center.
• The pupil is the black dot in the eye that dilates (gets bigger) in the dark and constricts (gets smaller) in light.
• The PD is usually NOT the same as the Eye Size of the glasses.

Types of PD measurements

Binocular & Monocular

A PD (Pupillary Distance) measurement can be provided in two formats: Binocular or Monocular. It may also be specified for either Distance or Near vision. In most cases, the PD refers to the Distance vision, and the Near PD is derived from the Distance PD by subtracting 2-3 millimeters.

The Binocular PD is typically a single number, but it may also be written with the Near PD included. Not to be confused with the Monocular PD, which is generally half of the Binocular Distance value, and for each eye, as shown in the example, and explained further below.
 

Binocular PD

The Binocular PD is one number — the total distance, in millimeters, between the centers of your pupils — measured from one pupil to the other across the bridge of the nose. It is the most common PD used for single vision lenses and general prescriptions.

Example: If your binocular PD is 63 mm, it means the total distance between your pupils is 63 mm. 

Monocular PD

The Monocular PD contains two numbers that measure the distance from the center of your nose (bridge) to each pupil individually. It's especially important when fitting progressive lenses, high prescriptions, or when the wearer's facial features are asymmetrical. When the monocular PD is the same in both eyes, they may be added together to combine one number or the Binocular PD measurement.

Example: Instead of one number, you’ll have two — like 32 mm (right eye) / 31 mm (left eye) — still adding up to 63 mm total, but allowing for more precision in lens alignment.

Near PD

Near Pupillary Distance (Near PD) is derived from the Distance PD and usually isn't provided by the customer. However, if it's included on a prescription, it's often written after the Distance PD (e.g., 63 / 60), where the second number is the Near PD. To estimate the Near PD, 2–3 mm is typically subtracted from the Distance PD. For monocular Near PD, this reduction is applied evenly to each eye.

Binocular Example: If your Distance Binocular PD is 63 mm, it means the near PD is usually 60.
Monocular Example: If your Distance Monocular PD is 32/31 mm, it means the near PD is usually 30.5/29.5 mm.

Locating your PD measurement

It can be a challenge to locate

The PD may not always be specified on the actual prescription, as the eye doctor doesn't always manufacture the glasses. This measurement is usually taken by the optical store that makes the glasses and crafts the lenses. Since the PD measurement is classified as a dispensing tool, rather than being part of the actual prescription, it is not typically tested during an eye exam.

To locate your PD measurement, you can try:

1. Check the prescription in case it was provided by the doctor.
2. Contact the last place your glasses were made, as they may possibly still have this in their files.
3. Have it measured again (See below)

How to Measure Your PD

Choose from 3 options below

Option 1: Measure with a Ruler

To measure the PD yourself at home with a ruler:

1. Stand and look straight at a mirror about 8–12 inches away.
2. Hold a millimeter ruler against your brow.
3. Close your right eye and align 0 mm with the center of your left pupil.
4. Open your right eye and close your left.
5. Read the millimeter mark aligned with your right pupil.
6. That number is your binocular PD.
7. Repeat a few times to ensure consistency.

Tip: Have a friend help for greater accuracy.
 

Option 2: Mobile PD Apps

To measure your PD using the camera on your phone or device, you can check your device's app store.
Quick links for "PD Measurement" Apps:

  

Please note that although these apps can be convenient, we are not affiliated with any specific app or guarantee their results. As accuracy may vary, we recommend:

• Using the best lighting possible
• Holding the phone at eye level
• Follow the instructions in the app
• Taking multiple readings and trying different apps for consistency

Option 3: Professional Measurement

The most accurate method is to have your PD measured by an eye care professional using:

• A PD stick (millimeter ruler)
• A pupillometer (a device that uses light reflection for precision)

Common PD Values & Ranges

Adults, children, and adolescents

PD Changes & Renewals

Keeping your PD up to date

In most healthy adults, the PD remains fairly stable and doesn't need to be remeasured once growth is complete. However, a PD can change during adulthood, such as due to surgery, injury, or changes in the facial structure.

For Children, the PD should typically be remeasured once a year, due to their developing facial structure. However, more frequently, if the child has a significant growth spurt, is getting new glasses, or starts reporting blurry vision.