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How to Measure your PD

If you haven’t ordered prescription eyeglasses online before, the first time may feel a little daunting—especially when you come across unfamiliar terms like pupillary distance. Don't worry, we have you covered.

What is Pupillary Distance (PD)?

Pupillary distance (PD) refers to the precise distance between the centers of the pupils of both eyes, typically measured in millimeters. Although this measurement may seem insignificant, it is crucial in the eyewear fitting process, as it determines whether the optical centers of the lenses can be accurately aligned with the visual axes of both eyes, thereby ensuring clear and comfortable vision.

  • Single PD

    Typically, your PD measurement will only have one number, known as a single PD, monocular pupillary distance (sometimes referred to as binocular pupillary distance), which is the distance from the center of each pupil to the bridge of the nose. This can be used to order most types of prescription eyewear.

  • Dual PD

    If your two readings are different, this is known as the double PD, binocular pupillary distance (sometimes also referred to as the binocular pupillary distance), which is the total distance between the centers of both pupils. In this case, these two readings represent the distance from each pupil to the bridge of the nose—the first number indicates the distance for the left eye, and the second number indicates the distance for the right eye. When added together, these two numbers should equal the total distance between your left and right pupils.

Printable PD Ruler

Print this page on A4 paper at 100% scale (do not resize). Use the PD ruler located at the bottom of the page. For the most accurate results, we recommend using a physical PD ruler or consulting your eye care professional.

⇩ DOWNLOAD EYDOLOGY'S PD RULER
Note: Please Print on A4.

How to Measure Your PD？

You can often get your PD measurement from your doctor or a licensed optician. However, pupillary distance is also easy to measure yourself! With a pupillary distance ruler (in other words, any millimeter ruler), you can measure the distance between the center of your pupils yourself in a mirror or have a friend help out.

  • Step 1

    Step 1

    Choose a ruler, sit or stand about 20 centimeters (8 inches) away from a mirror, or ask a friend to help you from an arm's length away. To ensure accuracy, repeat the measurement 2-3 times.

  • Step 2

    Step 2

    Close your right eye and align the “0” mark on the ruler with the center of your left pupil.

  • Step 3

    Step 3

    Close your left eye and read the number directly above your right pupil. This number is your total PD.

  • Step 4

    Step 4

    To obtain two independent pupil diameter values (one for each eye), measure the distance from the center of each pupil to the center of the bridge of your nose. This will be helpful if you need dual pupil diameters (OD and OS).

💡Tips：

  1. If the two measurements are the same, this indicates a single PD value. In this case, simply add the two measurements together to obtain the single PD value.
  2. To ensure accuracy, measure multiple times to confirm consistent results. You certainly want it to be precise. The average range for adult PD is 54–74 millimeters, and for children, it is 43–58 millimeters.

How to fill in PD?

Two of the same number (e.g. 30/30): This is the same as a Single PD measurement between the pupils. When entering this information to order your glasses, you can just add these together and we’ll automatically divide it equally.

Two low numbers (e.g. 30/31): The first number is the monocular PD for the right eye (O.D.) and the second number is for the left eye (O.S.).

Two high numbers (e.g. 62/59): This is used only for reading glasses. The first number is your Distance PD and the second number is your Near PD.

Please keep in mind that the PD is not always given as part of your prescription when you have an eye exam. If it’s missing, don’t worry, we can help.

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