PD stands for pupillary distance. It is one of the most important measurements used when making prescription glasses, yet it is also one of the most common reasons customers get stuck when ordering online. Your prescription may show SPH, CYL, AXIS and ADD clearly, but the PD measurement may be missing completely.
That can feel frustrating, but it does not automatically mean anything is wrong. A glasses prescription tells us the optical correction you need. PD helps decide where that correction should sit in the lenses once a frame has been chosen. Those are connected, but they are not the same thing.
The simple rule
PD is not a random checkout detail. It helps position the optical centres of your lenses in front of your eyes. If the measurement is wrong, the glasses may look fine but feel uncomfortable, especially with stronger prescriptions.
What is PD?
PD means pupillary distance. It is the distance between the centres of your pupils, measured in millimetres. Your pupils are the dark centres of your eyes. When prescription lenses are made, the laboratory needs to know where your eyes sit so the optical centres of the lenses can be positioned correctly.
For many single vision glasses, PD is the main horizontal measurement needed alongside the prescription. For varifocals, it is still essential, but it is only part of the fitting process. Varifocal lenses also need fitting heights because the lenses contain distance, intermediate and reading zones.
PD is part of the optics, not a formality.
Customers often see PD as a small detail because it is only one number. It is not. It tells us where your eyes sit in relation to the lenses. Lower prescriptions are usually more forgiving, but with stronger prescriptions, accuracy becomes much more important.
Why does PD matter when ordering glasses?
Prescription lenses are made so the correct optical area sits in the right place for your eyes. If the optical centres are not aligned properly, the glasses may feel uncomfortable even if the prescription values are technically correct.
An incorrect PD can create unwanted prismatic effect. In simple terms, your eyes may have to work harder than they should. Some people notice blur, pulling, headaches, eye strain or a strange feeling that the glasses are nearly right but not quite comfortable.
Usually more forgiving
Small PD differences may be less noticeable, but the measurement still matters if you want the lenses made properly.
Less room for error
As lens power increases, incorrect positioning can become more noticeable and more uncomfortable.
Why is my PD not on my prescription?
Many customers assume their optician has forgotten to include PD, but that is not always the case. In many situations, the prescription you receive after an eye test shows the lens powers needed, not every dispensing measurement needed to make a specific pair of glasses.
Think of it this way: the prescription tells us what correction your eyes need. The PD helps decide where that correction should sit in the lenses. The frame, lens type and purpose of the glasses can all affect the measurements needed.
What power?
SPH, CYL, AXIS, ADD and prism values tell us the optical correction required.
Where horizontally?
PD helps position the optical centres from left to right in the lenses.
Where vertically?
Fitting height is especially important for varifocals and some specialist lenses.
A prescription is not the same as a dispensing record
Your prescription explains the lens power. Your dispensing measurements help position those lenses in a chosen frame. This is why PD may not be shown on your prescription card, even though it still matters when ordering glasses.
“My prescription does not have a PD.”
This is one of the most common concerns customers have before ordering online. It is completely understandable, but it does not mean you are stuck. The important thing is to ask for help rather than guessing a number just to complete checkout.
Single PD vs dual PD
PD can be written in two common ways: single PD and dual PD. A single PD is one number, such as 62mm. This is the total distance between the centre of one pupil and the centre of the other.
A dual PD gives a separate measurement for each eye, usually from the centre of the bridge of the nose to each pupil. For example, 31/32 means one eye is 31mm from the centre line and the other is 32mm from the centre line.
| PD type | Example | What it means |
|---|---|---|
| Single PD | 62mm | The full distance between both pupil centres. |
| Dual PD | 31/31 | Each eye sits evenly from the centre line. |
| Dual PD | 30/32 | Each eye is measured separately because faces are not always perfectly symmetrical. |
Dual PD can be more accurate because faces are not perfectly symmetrical. One eye may sit slightly further from the nose than the other. That is normal. It simply means the lenses should be positioned to match your actual eye position.
Do not assume both eyes are exactly equal.
Some customers split a single PD in half because it feels logical. Sometimes that is acceptable, but not everyone is symmetrical. If accuracy matters, especially with stronger prescriptions, dual PD is better than a rough split.
Distance PD vs near PD
Your PD can vary depending on whether you are looking far away or looking up close. When you look at something near, your eyes turn slightly inward. This means a near PD is usually smaller than a distance PD.
Distance glasses usually use a distance PD. Reading glasses may use a near PD. Varifocals require more careful measurements because the lenses include several viewing zones in one design.
For looking far away
Used for distance glasses, driving glasses and general everyday distance correction.
For reading and close work
Usually smaller because your eyes turn inward when focusing on something close.
This is why using a random PD from an old order can be risky. You need to know whether it was a distance PD, near PD, single PD, dual PD or a measurement linked to a specific pair of glasses.
What is an average PD?
Average PD figures are often searched online, but they are not a safe substitute for your own measurement. Your glasses should be made for your eyes, not for an average person.
The problem with average PD is that it gives a number that feels reassuring without confirming anything about your face, your eyes, your frame or your prescription. Two people can have the same prescription and completely different PD measurements.
Using an average PD because it seems close enough
Average measurements are useful for general understanding, not for making your own glasses. If you are ordering prescription eyewear, use a proper measurement rather than a population average.
Why guessing your PD is risky
Guessing PD is tempting because it feels like a small shortcut. If checkout asks for one number and you do not know it, it is easy to search online, use an average, or estimate it from a mirror. The issue is that a small shortcut before ordering can create a bigger problem after the lenses are made.
If the PD is significantly wrong, the glasses may feel uncomfortable even if the prescription values were entered correctly. You might experience strain, pulling, blur, headaches, or a feeling that your eyes are working harder than they should.
Eyestrain
Your eyes may work harder if the optical centres are not aligned correctly.
Headaches
Incorrect lens positioning can contribute to discomfort or headaches for some wearers.
Poor adaptation
The glasses may feel strange even when the prescription power itself is correct.
If you do not know your PD, say so.
That is much better than guessing. A good online eyewear service should help with measurements rather than force you to invent a number. The danger is not admitting you do not know it; the danger is pretending you do.
How frame choice affects PD
PD is measured from your eyes, but the final result is affected by the frame. A frame that is too wide can place your eyes too far inward within the lenses. A frame that is too narrow can create the opposite issue. Even with an accurate PD, the chosen frame still needs to make sense for your face and prescription.
This is why your eyes should sit reasonably central in the lenses. They do not have to be perfectly central in every fashion frame, but they should not sit dramatically toward the inner or outer edge. Poor eye position within the lens can affect comfort, lens thickness and appearance.
Frame and PD fit checklist
- Your eyes should sit reasonably central in each lens
- The frame should not be much wider than your face
- The bridge should hold the frame at the correct height
- Strong prescriptions usually need more careful frame choice
- Very oversized frames can make lens positioning and thickness harder to manage
- Varifocals need both horizontal and vertical measurements
PD for varifocal lenses
Varifocals are different from standard single vision glasses because they contain more than one viewing zone. The top part of the lens is used for distance, the middle area for intermediate vision and the lower area for reading. Because of this, positioning is more critical.
For varifocals, PD alone is not enough. Fitting height is also needed. This tells the laboratory where the varifocal design should sit vertically in the frame. The frame also needs enough depth to hold the lens design properly. Very shallow frames may not give enough room for comfortable varifocal zones.
PD is usually the key measurement
For distance or reading glasses, PD is normally the main positioning measurement needed alongside the prescription.
PD plus fitting height
Varifocals need more detail because the lens has multiple zones. Frame fit and height matter.
Do not order varifocals using guessed measurements
Varifocals are not the place to cut corners. If the measurements are wrong, the reading area, intermediate area or distance zone may not sit where your eyes expect them to be.
How Burghley & Co helps with PD
At Burghley & Co, the aim is not to leave you stuck at checkout guessing numbers. If you do not know your PD or your prescription card looks incomplete, you can ask for help before the lenses are made. That is the correct way to handle online prescription eyewear.
For many single vision orders, the process is straightforward once the prescription and PD are confirmed. For varifocals and more complex orders, additional fitting information may be needed. The important point is that the order should be reviewed before glazing rather than treated as a blind automated transaction.
Choose your frame
Select a frame that suits your face, prescription and the type of lenses you need.
Provide your prescription
Enter the prescription details carefully or send a clear image of your prescription card.
Confirm measurements
If PD or fitting details are missing, they can be checked before the lenses are made.
Your order is reviewed
The prescription, lens choice and measurement requirements are considered before glazing.
Common PD myths
PD does not matter for low prescriptions
Lower prescriptions are usually more forgiving, but PD still matters if you want the glasses made properly.
You can just use the average
Average PD is not your PD. It should not be used as a substitute for a real measurement.
PD never changes
Adult distance PD is usually stable, but near PD, frame fit and lens requirements can differ.
My prescription includes everything
Your prescription gives lens power. It may not include all dispensing measurements needed for a specific frame.
PD is only needed for varifocals
Single vision glasses also need accurate positioning, especially with stronger prescriptions.
One PD works for every task
Distance and near measurements can differ, so the use of the glasses matters.
Quick decision guide
Not sure what to do with your PD?
When should you ask for help?
You should ask for help if you do not know your PD, if your prescription includes prism, if your prescription is strong, if you have a large difference between the two eyes, if you are ordering varifocals, or if your previous glasses caused adaptation problems.
You should also ask if the frame you like is very large, very shallow or significantly different from your current pair. The more the frame changes, the more important it is to think about fit and positioning before ordering.
Ask before ordering if:
- Your prescription card does not show PD
- You are not sure whether your PD is distance or near
- You have prism in your prescription
- Your prescription is stronger than average
- You are ordering varifocals
- You have had problems adapting to glasses before
- You are choosing a much larger frame than usual
- Your prescription details look confusing
The right time to ask is before the lenses are made.
Once lenses have been glazed into a frame, mistakes become harder and more expensive to fix. If you are unsure about PD, prescription values or frame suitability, ask before ordering. That is not being difficult; that is being sensible.
Final PD checklist before you order
Before placing an online prescription glasses order, use this checklist. It will help you avoid the most common measurement mistakes.
PD order checklist
- I know whether my PD is single or dual
- I know whether the measurement is for distance or near use
- I have not used an average PD from the internet
- I have not guessed my PD from a mirror
- I have checked that my frame size is sensible for my face
- I understand that varifocals need fitting height as well as PD
- I have asked for help if my prescription is strong or complicated
- I have provided a clear prescription image if I am unsure
Still unsure about your PD?
Send Burghley & Co a clear copy of your prescription before ordering and we can advise on what measurements are needed for your chosen frame and lenses.
Frequently asked questions
What does PD mean?
PD means pupillary distance. It is the distance between the centres of your pupils, measured in millimetres. It helps position the optical centres of your lenses correctly.
Why is PD important for glasses?
PD matters because prescription lenses need to line up with your eyes. If the optical centres are positioned incorrectly, the glasses may feel uncomfortable or harder to adapt to, especially with stronger prescriptions.
Why is my PD not on my prescription?
Your prescription usually shows the lens power required for each eye. PD is a dispensing measurement used to position the lenses, so it is not always included on the prescription card given after an eye test.
Can I measure my own PD?
Some tools and guided processes can help, but you should not guess. If you are unsure, ask for help before ordering rather than using a rough estimate.
Is single PD or dual PD better?
Dual PD is often more precise because it gives a separate measurement for each eye. A single PD gives the total distance between both pupils.
Is near PD the same as distance PD?
No. Near PD is usually smaller because your eyes turn inward when looking at something close. Distance glasses and reading glasses may use different measurements.
Do I need PD for reading glasses?
Yes, reading glasses still need correct positioning. The measurement used may be a near PD rather than a distance PD, depending on the lens and prescription.
Do I need PD for varifocals?
Yes, but PD alone is not enough. Varifocals also need fitting height and a suitable frame because the lenses contain distance, intermediate and reading zones.
Can I use the PD from my old glasses?
Possibly, but only if you know what the measurement was, what it was used for and whether it is suitable for the new glasses. If in doubt, get it checked.
What happens if my PD is wrong?
If PD is wrong, the lenses may not line up correctly with your eyes. This can cause discomfort, eyestrain, blur, headaches or a feeling that the glasses are not quite right.
Need help?
Unsure what to choose?
If you are not sure about your prescription, frame size or lens choice, ask before you order.