If you are ordering prescription glasses online, you may be asked to enter your pupillary distance, commonly called PD. While your eyeglass prescription includes information such as SPH, CYL, AXIS, and ADD, PD is not always written on the prescription.
Fortunately, pupillary distance is relatively easy to measure at home. In this guide, we explain what PD means, why it matters, how to measure it yourself, and how to avoid some of the most common measurement mistakes.
On This Page
- What Is Pupillary Distance (PD)?
- Why Is PD Important for Glasses?
- Where Can You Find Your PD?
- How to Measure Your PD at Home
- How to Measure PD With Someone Else's Help
- Single PD vs. Dual PD
- What Is the Average Pupillary Distance?
- How Accurate Does PD Need to Be?
- Common PD Measurement Mistakes
- PD for Progressive Lenses
- Pupillary Distance FAQs
What Is Pupillary Distance (PD)?
Pupillary distance is the distance, measured in millimeters, between the centers of your pupils.
For example, if the distance between the center of your right pupil and the center of your left pupil is 63 millimeters, your PD would normally be written as 63 mm.
PD helps determine where the optical center of each prescription lens should be positioned relative to your eyes. Correct lens positioning helps you look through the intended portion of the lenses.
Why Is PD Important for Prescription Glasses?
Your prescription tells the lens manufacturer the corrective power your lenses need, while your pupillary distance helps determine where that corrective power should be positioned in front of your eyes.
An inaccurate PD measurement can cause the optical centers of the lenses to sit too far inward or outward. Depending on the prescription and the amount of difference, this may contribute to discomfort such as:
- Eye strain
- Headaches
- Difficulty focusing
- Visual discomfort
- A feeling that the lenses are not properly aligned
PD becomes especially important with stronger prescriptions and more complex lens designs because proper lens positioning has a greater effect on visual comfort.
Where Can You Find Your PD?
Before measuring your PD yourself, check whether you already have the measurement. PD may appear on an eyeglass prescription, optical receipt, previous glasses order, or patient record from your eye doctor or optical store.
It may be listed as:
- PD
- Pupillary Distance
- Distance PD
- A single number such as 63
- Two numbers such as 31 / 32
If your prescription does not show your PD, you can ask your optician or eye-care provider whether they have the measurement on file. You can also measure it at home.
How to Measure Your PD at Home
One of the easiest ways to measure pupillary distance yourself is with a millimeter ruler and a mirror.
What You Will Need
- A ruler with millimeter markings
- A mirror
- Good lighting
Step-by-Step PD Measurement
-
Stand approximately 8 inches from a mirror.
Keep your head straight and look directly ahead. -
Hold the ruler horizontally across your face.
Position it just above or directly in front of your eyes without blocking your vision. -
Align the 0 mm mark with the center of one pupil.
Keep the ruler as straight and level as possible. -
Look at the center of your other pupil.
Read the millimeter measurement that lines up with its center. -
Write down the measurement.
For example, if the second pupil lines up with 63 mm, your total PD is 63 mm. -
Repeat the measurement two or three times.
Repeating the process helps confirm that your measurement is consistent.
How to Measure PD With Someone Else's Help
If possible, asking another person to measure your PD can make the process easier.
- Sit or stand directly in front of the person helping you.
- Look straight ahead at a distant object rather than directly at the ruler.
- Have the person hold a millimeter ruler horizontally in front of your eyes.
- Align the 0 mm mark with the center of one pupil.
- Measure to the center of the other pupil.
- Repeat the measurement to confirm the result.
Keeping your eyes focused straight ahead can help prevent your eyes from converging inward while the measurement is being taken.
Single PD vs. Dual PD: What's the Difference?
You may encounter two different ways of recording pupillary distance: single PD and dual PD.
| PD Type | Example | What It Means |
|---|---|---|
| Single PD | 64 mm | Total distance from the center of one pupil to the center of the other. |
| Dual PD | 31 / 33 mm | Distance from the center of the nose to each pupil, measured separately. |
For example, if your right-eye PD is 31 mm and your left-eye PD is 33 mm, your total PD would be:
31 + 33 = 64 mm
Dual PD can provide more precise information because a person's face is not always perfectly symmetrical.
What Is the Average Pupillary Distance?
Adult pupillary distance commonly falls somewhere around the low-to-mid 60 mm range, but there is considerable natural variation between people.
Your PD may be smaller or larger depending on your facial structure, and a measurement outside an average range does not automatically mean it is incorrect.
How Accurate Does PD Need to Be?
PD should be measured as accurately as reasonably possible. A difference of a fraction of a millimeter is generally less concerning than being several millimeters off.
How much an inaccurate PD affects vision depends on several factors, including:
- Your prescription strength
- The type of lenses
- The frame size and shape
- The amount of PD measurement error
- How sensitive you are to changes in lens positioning
People with stronger prescriptions may be more sensitive to an inaccurate measurement, which makes careful PD measurement particularly important.
Common PD Measurement Mistakes
Most at-home PD measurement problems come from positioning rather than the ruler itself.
1. Holding the Ruler at an Angle
The ruler should remain horizontal. Tilting it upward or downward can change the measurement.
2. Measuring From the Edge of the Pupil
PD is measured from the center of one pupil to the center of the other, not from the inner or outer edges.
3. Moving Your Head While Measuring
Keep your head upright and facing forward during the entire measurement.
4. Looking Sideways
Your eyes should look straight ahead. Looking toward the ruler or to one side can slightly change the apparent pupil position.
5. Measuring Only Once
Take the measurement several times. If you get 62 mm, 67 mm, and 64 mm, something is probably changing between measurements and you should try again.
6. Confusing PD With Frame Measurements
Numbers printed inside your eyeglass temples — such as 52-18-140 — describe frame dimensions. They are not your PD.
If you're not sure what those numbers mean, read our guide: What Do the Numbers on My Glasses Mean?
Do Progressive Lenses Need PD?
Yes. Pupillary distance is important when making progressive lenses because the different viewing zones of the lens must be positioned correctly in relation to your eyes.
Progressive lenses contain multiple viewing areas for distance, intermediate, and near vision rather than having one prescription power across the entire lens. Because of this, proper lens positioning is especially important.
Depending on the progressive lens design and the optical lab, additional measurements such as fitting height may also be used.
If you're still deciding which type of lens you need, our Single Vision vs. Progressive Lenses guide explains the main differences.
Does PD Change Over Time?
For most adults, pupillary distance remains relatively stable because the basic structure of the face has finished growing.
Children's PD can change as they grow, so an older childhood measurement should not automatically be used for new glasses years later.
If you are unsure whether an older PD measurement is still appropriate, it is easy to measure again before ordering new glasses.
Can I Measure PD With a Phone App?
There are smartphone apps and online tools designed to estimate pupillary distance. These can be convenient, particularly when you do not have someone available to help.
However, results can depend on factors such as camera position, lighting, calibration, and how the phone is held. If you use an app, consider comparing the result with a manual ruler measurement.
Frequently Asked Questions About Pupillary Distance
Is PD normally written on an eyeglass prescription?
Not always. Your prescription may contain SPH, CYL, AXIS, and ADD values without listing pupillary distance. Your optician may have your PD recorded separately.
What does a PD of 63 mean?
A PD of 63 means the distance between the centers of your pupils is approximately 63 millimeters.
Is PD the same as the bridge size of my glasses?
No. Bridge width is a physical measurement of the eyeglass frame. PD measures the position of your eyes and is used when positioning prescription lenses.
Can I use an average PD when ordering glasses?
It is better to use your actual PD rather than an average. People's facial proportions vary, so an average measurement may not match your eyes.
Should I measure my PD more than once?
Yes. Measuring two or three times is a good way to make sure you are getting a consistent result.
Do I need separate right and left PD measurements?
Not necessarily. Many prescriptions and glasses orders use a single total PD. Some lens designs or prescriptions may benefit from separate monocular measurements for the right and left eyes.
Does PD matter for non-prescription glasses?
PD is primarily used to position prescription lens optics. It generally is not required when ordering frames with non-prescription or demo lenses.
Ordering Prescription Glasses Online With Your PD
Once you have your prescription and pupillary distance, ordering prescription glasses online becomes much easier.
When entering your prescription information, carefully double-check your SPH, CYL, AXIS, ADD, and PD values before submitting your order. Small details matter when lenses are being customized specifically for your eyes.
At Youtop Optical, we offer a variety of prescription lens options, including single vision and progressive lenses as well as multiple lens indexes and optional coatings.
If you are unsure which lens thickness is appropriate for your prescription, you can also read our guide: 1.56 vs. 1.61 vs. 1.67 vs. 1.74 Lenses: Which Lens Index Should You Choose?