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The pupillary distance (PD) measurement is a requirement for people who want to purchase eyeglasses. Some eyewear manufacturers provide how-to videos to help customers calculate their PD without visiting an eye doctor’s clinic.
This article describes what PD is and explains the different measuring methods individuals can use.
PD refers to the distance in millimeters (mm) between the centers of the pupils in the eyes.
This measurement helps manufacturers prepare prescription glasses, as it ensures that the prescription aligns with the person’s eyes. PD indicates exactly where the individual will look through the lenses of their glasses.
There are two types of PD. Far PD refers to the distance between the pupils when a person is viewing a distant object. Eye doctors use this type of PD for distance vision glasses. Near PD is the distance between the pupils when an individual is looking at a near object, such as when reading.
It is important to measure PD correctly. The Canadian Association of Optometrists states that inaccuracies in PD measurements can lead to:
- distorted vision
- blurred vision
(Video) How to Measure Your PD (Pupillary Distance) with SelectSpecs (HD)
According to a 2016 study, PD can vary among individuals. The researchers note that various factors, including age, sex, and ethnicity, can influence the measurement.
The researchers also state that this measurement can increase until a person’s mid-20s. After this age, PD tends to remain constant.
The authors of a
There are no studies investigating the average PD for children. However, some companies that sell eyeglasses use a default measurement if a parent or caregiver does not know the child’s PD.
Most children’s PD is 43–58 mm, and eye care professionals can measure this distance during an eye exam.
There are two types of PD measurements: single PD and dual PD.
Single or binocular PD measurement refers to the distance between the center of one pupil and the center of the other. A single PD measurement provides one number, such as 60, 63, or 55 mm.
Dual or monocular PD refers to the distance between each pupil’s center and the bridge of the nose. Dual PD measurements include two numbers. For example, if the dual PD is 31/33, the first number would refer to the right eye, and the second would refer to the left eye.
The American Academy of Ophthalmology notes that some prescriptions may also include the abbreviation OD or OS. OD is short for oculus dexter, which refers to the right eye, and OS is short for oculus sinister, which refers to the left eye.
Learn how to read an eye prescription.
A person can measure their PD by using a ruler. Here is a step-by-step guide on doing this:
- Stand up straight, about 8 inches from a mirror.
- Hold a ruler against the eyebrows and close the right eye to align the ruler’s 0 mm marker with the left pupil’s center.
- While looking straight ahead, open the right eye, close the left one, and check the value on the ruler above the right pupil’s center.
- The resulting measurement is the single PD.
Individuals can also measure their single PD with the help of another person. The individual who requires a measurement can look at an object approximately 20 feet away from them. The person measuring can align the ruler’s 0 mm mark with the center of one pupil and then measure to the other pupil’s center.
To calculate a dual PD, people need to measure from one pupil to the bridge of the nose, note the measurement, and then do the same for the other eye.
People should take several single and dual PD measurements and calculate the average distance to ensure a more accurate result.
People who already wear eyeglasses can find their PD by following these steps:
- Put the glasses on.
- Ask another person to stand in front of them.
- Using a non-permanent marker pen, mark two dots on the glasses above the left and right pupils.
- Measure the distance between these two dots with a ruler.
This measurement is a person’s PD. People may wish to perform these steps several times to ensure a more accurate result.
Once a person knows their single PD, they can calculate their near PD by removing 3 mm.
For example, someone with a single PD of 60 mm would have a near PD of 57 mm.
Alternatively, a person can use their dual PD and subtract 1.5 mm from each eye’s measurement. For someone with a dual PD of 31/33 mm, the result would be 29.5/31.5 mm.
It is important to know what a person’s PD is to ensure that their glasses fit correctly. An optician can measure PD when fitting glasses. However, a person who buys glasses online may need to measure their PD at home.
Please note that the writer of this article has not tried these products. All information presented is purely research-based and correct at the time of publication.
Medical News Today follows a strict product selection and vetting process. Learn more here.
People can choose from a range of companies that sell glasses online. The following companies offer a service that allows a customer to see how frames look on them before they commit to a purchase. They also have a generous returns policy in case a person measures their PD incorrectly.
- Warby Parker: This company allows people to try on up to five frames for free at home. Warby Parker also offers a 30-day refund or exchange policy and a 1-year no-scratch guarantee on their lenses. Learn more about Warby Parker.
- Zenni Optical: This company has a virtual try-on service that allows people to get an idea of which frames would suit them. Zenni Optical also offers a 30-day returns policy for store credit. Learn about Zenni Optical.
- EyeBuyDirect: This company allows people to upload photos and take a quiz to decide which frames may be most suitable for their face shape. EyeBuyDirect offers a 14-day fit and style guarantee with a one-time replacement or refund. Its glasses also come with a 365-day product guarantee that allows customers to claim a one-time replacement pair if the glasses are defective. Learn more about EyebuyDirect.
Here, we answer some frequently asked questions about measuring PD.
Is there an app to measure PD?
People can also ask an eye care professional to measure their PD during an eye exam.
Can you measure PD from old glasses?
Yes, a person can measure their PD using their old glasses. They will need another individual to help them by placing two dots on the glasses above the left and right pupils.
People can then measure the distance between these dots.
What happens if my PD measurement is off?
If a person does not have a correct PD measurement, it can affect the usefulness of glasses, especially progressive lenses.
Someone who is unsure of their PD measurement may wish to contact an eye care professional to accurately measure the distance between their pupils.
(Video) How to Measure Your PD (Pupillary Distance) At Home With Mobile, Ruler or Tape Measurement-Specscart
PD measures the space between a person’s pupils to ensure that their glasses and lenses fit correctly. Opticians will measure an individual’s PD when they are fitting glasses. Alternatively, a person can measure their PD at home.
People who purchase glasses online may wish to buy from companies that have a generous returns policy in case they mismeasure their PD, which would make their glasses less effective.
We recommend you get your pupil distance measurement using a free pupil distance app. The two PD apps we recommend are Glasses On which you can download from the Google Play store for Android or Eye Measure which can be downloaded from the Apple App Store for iPhone.Can you measure PD from old glasses? ›
Grab your old glasses and a non-permanent marker pen. Get your partner to mark a small dot where your pupil is behind the lens. Measure the distance between the dots for your total PD.Why is my PD not on my prescription? ›
Some offices will put the PD measured by some of the instrumentation during your exam on the prescription and others will have the optician take that measurement for you. The doctor during your exam does not take your PD at anytime during your exam, as that is left to the optician who is going to make your eyewear.Does PD have to be exact? ›
The pupillary distance measurement does not have to be 100% precise to be useful, as it can tolerate a fairly small error range. If you do measure your own pupillary distance, it is recommended that you try several attempts to be sure you get a fairly accurate measurement.What happens if the PD on my glasses is wrong? ›
PD means “pupillary distance,” which is the distance between the center of each pupil. This measurement is used to determine where you look through the lens of your glasses. If the PD is wrong, or as we say in the optical world “out of tolerance,” you won't be able to focus your eyes together properly.Is it hard to measure PD? ›
Whenever possible, we recommend getting your PD measurement from your eye care professional. But don't worry if they didn't include it on your glasses prescription – it's easy to measure PD by yourself. Just make sure to take your time and do it at least twice, to ensure it's accurate.What if my PD is off by 2mm? ›
WHAT IF MY PD IS OFF BY 2mm? Even a 2mm difference in pupillary distance can cause a pair of eyeglasses to feel off because your pupils tend to converge or diverge to the center of the lens. Moreover, pupillary distance is more crucial on the higher the power of your prescription.Do opticians have to tell you your PD? ›
Why does the optician not give me my pupillary distance? Your ophthalmic practitioner or optometrist is not required by law to include details of the horizontal distance between your pupils (the inter-pupillary distance) in your prescription.How do I find my PD number for my glasses? ›
Face your friend and look straight ahead with both eyes open. Have your friend hold the ruler up to your right so the zero end lines up with your pupil. Measure the distance from your right to your left pupil. The number that lines up with your left pupil is your PD.Can you order glasses without PD? ›
Before you start browsing online, you'll need two sets of numbers – your new EyeGlass Numbers and your Pupillary Distance (PD) measurement. PD is a measurement that's often left off of your issued prescription, yet without an accurate PD, your new glasses won't do their job.
Pupillary distance is measured in millimetres, and is sometimes expressed as 'PD' on your prescription. Your pupillary distance can change during childhood and adolescence, but will almost certainly remain the same once you reach adulthood. The average pupillary distance for adults is between 50 and 70mm.What is the most common PD for glasses? ›
Pupillary distance (PD) measures the distance between the centers of your pupils. This measurement is used to determine where you look through the lens of your glasses and should be as accurate as possible. The average adult's PD is between 54-74 mm; kids' are between 43-58 mm.Does frame size affect PD? ›
Different frames affect PD because the size of the frames affects the optical center. This is especially true with larger lenses and frames. Finding a properly fitted frame for prescription lenses is just as important as getting an accurate PD measurement.What's the average PD for a woman? ›
The average PD for adult females is 62 mm, which is about 2.44 inches.Can I measure my PD with my phone? ›
PD Meter App by GlassifyMe
GlassifyMe's PD Meter App is available for both iOS and Android. All you need is a standard card with a magnetic strip (gift card, rewards cart, or points card) and you can measure your PD using the app in a few quick steps – without the need of a ruler.
The potential difference between points A and B, ΔV = VB – VA , is thus defined to be the change in potential energy ΔPE of a charge q moved from A to B, divided by the charge. Units of potential difference are joules per coulomb, given the name volt (V) after Alessandro Volta.Can PD be off by 2 mm? ›
WHAT IF MY PD IS OFF BY 2mm? Even a 2mm difference in pupillary distance can cause a pair of eyeglasses to feel off because your pupils tend to converge or diverge to the center of the lens. Moreover, pupillary distance is more crucial on the higher the power of your prescription.Why is PD the same in parallel? ›
Potential difference in parallel
Since potential difference is used to measure changes in energy, the potential difference supplied is equal to the potential differences across each of the parallel components but the value of current and resistance could be different.
V = k × [q/r]
V = electric potential energy. q = point charge. r = distance between any point around the charge to the point charge. k = Coulomb constant; k = 9.0 × 109 N.
And the voltage difference across the light bulb is: ∆V = I R = (0.06 A)(20 Ω) = 1.2 V ▪If we measure the voltage difference across the battery or the light bulb, we will get 1.2 V.
What is Pupillary Distance? Pupillary distance (PD) measures the distance between the centers of your pupils. This measurement is used to determine where you look through the lens of your glasses and should be as accurate as possible. The average adult's PD is between 54-74 mm; kids' are between 43-58 mm.Why do I have 2 numbers for my PD? ›
But if you have two different numbers, you have been measured for Dual PD (also known as monocular PD). In this scenario, the numbers are measurements of the distances from each pupil to the bridge of your nose - the first number refers to the left eye distance, and the second to the right.