How to Calculate Your PD?

Most of the time, when shopping for glasses online, there’s a section where you need to enter the Pupil Distance. Usually, the doctor or optician writes the PD on your prescriptions, but what if you’ve lost your prescription or the doctor has not mentioned the PD? No worries, as this guide comprises four methods by which you can calculate the PD at your home.

Accurate measurement of Pupil Distance (PD) is crucial if you are looking to get prescription eyeglasses. PD ensures that the lens aligns perfectly with your eyes, and if the PD measurements lack precision, even a well-crafted lens can cause discomfort and negatively affect your vision.

Continue reading to get detailed insights on calculating PD so that you can get the prescription glasses that provide the best vision and comfort.

What is Pupil Distance (PD)?

Pupil Distance (PD) is the measurement of distance between the pupils of the eyes. It is measured in millimeters (mm), and the measurement varies from person to person, depending on whether they are looking at the objects at a closer or farther distance.

Opticians or doctors often check the PD with an instrument called a “Pupillometer” while examining your eye. It is the most accurate way to measure PD. However, sometimes doctors do not write the PD measurements on the prescription, but there’s nothing to worry about, as there are some other ways.

Why Accurate PD Matters?

Before getting into why it’s crucial to get your PD measured, first understand how image forms in the eyes. After a light ray strikes the pupil, it travels through the lens. Here, the light bends to reach the retina, where the image is formed.

But if you have an impaired vision condition like myopia or hyperopia, the light does not bend correctly. In this case, prescribed eyeglasses are used to correct the bending of the light. These prescription eyeglasses have an optical center, which is the spot where the pupil looks through most of the time for optimal vision.

Therefore, the optical center of the lens must be aligned with the pupils so that you can make the most of your glasses. This is where PD comes into the picture, as it helps the providers in the correct positioning of the optical centers in front of pupils.  

Types of PD

Pupil Distance is of two types. For a better understanding, head over to this table of comparison:

How to Measure Your PD at Home?

Method 1: Measuring PD With A Ruler

1. Firstly, get a PD ruler and make sure that you are in a well-lit environment.
2. Then, stand at a distance of 8 inches from your mirror.
3. Place the PD ruleron your forehead in such a way that the 0mm point of the ruler aligns with the center of the pupil of your left eye.
4. Close your left eye and open your right eye.
5. Notice the point of the ruler that aligns with the center of your right eye’s pupil, which is your pupillary distance.

Method 2: Measuring PD With A Felt-Tip Marker and Glasses

1. Take a marker, but make sure that it’s not permanent because you will have to remove the marks straight after measuring.
2. Wear your eyeglassesand focus on any object that is placed at least 20 feet away.
3. On your right lens, mark a point with the marker on the top of the object.
4. Do the same on the left lens as well.
5. After that, focus on the object with both eyes to make sure that both dots overlap each other in your field of vision.
6. Then, take off your glasses and measure the distance between both marks with the help of aPD ruler.
7. The resulting measurement is your PD.

Method 3: Measuring PD With A Ruler and Friend

1. For this method, you don’t need to scratch your head when seeing measurements, as your friend will do it for you.
2. Start with placing a PD ruler horizontally above your eyebrows from the center of the pupil of your left eye.
3. Ask your friend to see the point on the ruler that aligns with the center of the pupil of your right eye.
4. The resulting count will be your PD.

Method 4: Measuring PD With Online Tools

1. Download an online PD measurement tool.
2. Follow the on-screen instructions and position your face within the frame.
3. Ensure that your face is steady, and align the markers with your pupils.
4. Rest for a few minutes, and the tool will calculate your PD.

Which PD is Considered Normal?

There is no such Pupillary Distance that fits in all shoes, as this number varies from person to person. However, the average PD distance is 60-64 mm for adults.

Final Words

All in all, calculating PD is a very easy-to-do task that can be performed at home with minimal objects. All you need is a PD ruler, or you can use an online PD calculator app. So, get your PD calculations done so that you can seamlessly shop for glasses online.