Ordering prescription glasses online is easier than ever—but accurate measurements are essential for clear, comfortable vision.
Besides your prescription, two key measurements affect how your lenses perform: PD (Pupillary Distance) and Segment Height. While PD ensures your lenses are centered with your eyes, segment height determines the vertical position of the optical zones within the frame.
In this guide, you'll learn what these measurements mean, why they matter, and when you actually need to provide them.
What Is PD (Pupillary Distance)?
PD (Pupillary Distance) is the distance, measured in millimeters, between the centers of your pupils.
This measurement allows the optical center of each prescription lens to align perfectly with your eyes, providing the clearest vision while minimizing eye strain.
There are two common types of PD:
- Single PD — One total measurement across both eyes.
- Dual PD — Separate measurements for each eye.
Most adults have a PD between 54 mm and 74 mm, although everyone's measurement is unique.
Why Is PD Important?
Even if your prescription is accurate, an incorrect PD can prevent your lenses from performing as intended.
An inaccurate PD may cause:
- Blurry vision
- Eye strain
- Headaches
- Difficulty focusing
- Reduced visual comfort
This is especially important for higher prescriptions and progressive lenses, where precise lens alignment makes a noticeable difference.
Taking a few minutes to measure your PD accurately helps ensure the best visual experience.
How to Measure PD for Glasses
Option 1: Check Your Prescription First
Before measuring your PD, check your eyeglass prescription. Many optometrists include your PD (Pupillary Distance) on the prescription.
If your PD is already listed, simply enter that value when placing your order—no additional measurement is necessary.
If you can't find it, you can easily measure your PD using our online Try On feature.
Option 2: Use Our Online Try On Tool (Recommended)
If your prescription doesn't include your PD, our Try On tool offers a quick and convenient way to measure it.
Simply:
- Open any product page.
- Tap Try On.
- Follow the on-screen instructions.
- Your PD will be measured automatically.
The entire process takes about one minute and requires no special equipment.
Option 3: Measure with a Ruler
If you prefer a manual method, you can measure your PD at home using a millimeter ruler and a mirror.
- Stand in front of a mirror.
- Hold the ruler across your eyebrows.
- Close one eye and align the "0" mark with the center of your other pupil.
- Switch eyes and read the measurement at the center of the second pupil.
- Repeat several times to confirm accuracy.
What Is Segment Height?
Segment Height (also called Fitting Height) is the vertical distance from the bottom of the lens to the center of your pupil while you're wearing the frame.
Unlike PD, segment height depends on the specific frame because it changes based on:
- Frame design
- Frame size
- Nose bridge fit
- How the frame sits on your face
For this reason, segment height is frame-specific, not person-specific.
This measurement is especially important for progressive lenses, bifocal lenses, and other multifocal lens designs, where different viewing zones are built into the lens. An accurate segment height helps position these zones correctly, providing smoother transitions between distance, intermediate, and near vision while improving overall comfort.
Do I Need to Provide Segment Height?
For most customers, the answer is no.
First-time purchase
If this is your first order with us, simply leave the segment height field blank.
Our experienced lab will calculate the appropriate fitting height based on your selected frame, prescription, and lens type.
Ordering a different frame
If you're purchasing a new frame style, you also don't need to provide segment height.
Since every frame fits differently, measurements from another frame usually aren't suitable.
Reordering the same frame
If you're ordering the same frame model again, providing your previous segment height is recommended.
Using the same measurement helps us reproduce your previous lenses more consistently, especially for progressive, bifocal, or anti-fatigue lenses.
How to Measure Segment Height
Although most customers don't need to provide this measurement, you can certainly do so if you'd like.
Method 1: Marker and Mirror
- Put on your glasses and adjust them so they sit naturally.
- Stand in front of a mirror and look straight ahead.
- Mark the center of each pupil on the demo lenses using a washable marker.
- Remove the glasses.
- Measure from the center of each dot to the lowest inside edge of the frame using a millimeter ruler.
Method 2: Visit an Optical Shop
For the most accurate result, you can also:
- Visit a local optical shop.
- Ask an optician to measure the fitting height while you're wearing the selected frame.
Please note: We currently do not offer an online tool for measuring segment height. Our online Try On feature measures PD only.
Common Measurement Mistakes
Avoid these common mistakes when measuring your glasses:
- Guessing your PD.
- Measuring in centimeters instead of millimeters.
- Tilting your head while measuring.
- Reusing segment height from a different frame.
- Assuming every pair of glasses has the same fitting height.
Small measurement errors can significantly affect the comfort and clarity of your prescription lenses.
Need Help?
If you're unsure about your measurements, we're here to help.
You can:
- Measure your PD using our online Try On tool.
- Upload your prescription during checkout.
- Contact our customer support before placing your order.
We'll review your information and ensure your lenses are produced using the most appropriate measurements.
Final Thoughts
Ordering prescription glasses online doesn't have to be complicated.
Your PD is a personal measurement that can often be found on your prescription or measured in minutes using our online Try On tool.
Segment height is different—it's specific to the frame you choose. In most cases, first-time customers or those ordering a different frame don't need to provide it, as our experienced lab will calculate the appropriate fitting height during production. If you're reordering the same frame, providing your previous segment height can help us deliver an even more consistent visual experience.
With accurate measurements and expert lens craftsmanship, you can order your prescription glasses online with confidence.
