How to Measure Your Pupillary Distance: A Guide for Big Heads

When you order prescription glasses for big heads, getting the right fit isn’t just about frame size—it’s also about making sure your lenses are positioned correctly in front of your eyes. This is where pupillary distance (PD) comes in.

What is PD?

Pupillary Distance (PD) is the measurement (in millimeters) between the centers of your pupils. This number helps ensure that your lenses align properly with your eyes, providing clear, comfortable vision.

Why is PD Important?

If your PD is incorrect, your lenses won’t be positioned correctly, which can lead to:

• Blurred vision – especially for higher prescription strengths.
• Eyestrain or discomfort – your eyes may struggle to focus if the lenses aren’t aligned.
• Distortion – particularly for progressive or bifocal lenses.

The Easiest and Most Reliable Way to Get Your PD

Since you already have a prescription, the fastest and most accurate way to get your PD is to contact the optician who provided your prescription. In most cases, this information was already measured during your eye exam, even if it wasn’t written on your prescription slip. Simply call or visit your optician and ask for your pupillary distance (PD) measurement—this ensures complete accuracy and removes any guesswork.

What If You Can’t Get Your PD from Your Optician?

If reaching out to your optician isn’t an option, don’t worry! You can still measure your PD yourself at home using a ruler or a mobile app. We’ll guide you through the best methods in the next section.

Measure Your Pupillary Distance Yourself (Step-by-Step Guide)

If you’re unable to get your pupillary distance (PD) from your optician, don’t worry—you can measure it yourself at home. All you need is a ruler with millimeter markings and a mirror (or a friend to assist). Follow these simple steps to ensure accuracy.

Step-by-Step Guide to Measuring Your PD

What You’ll Need:

• A ruler with millimeter (mm) markings
• A mirror
• Good lighting

Step 1: Stand in Front of a Mirror

Find a well-lit space with a mirror at eye level. Stand about 8–12 inches away to ensure clear visibility of your pupils.

Step 2: Position the Ruler Correctly

Hold the ruler horizontally against your forehead, just above your eyes. Align the "0 mm" mark with the center of your left pupil while keeping your head straight and level.

Step 3: Measure the Distance

Look straight ahead and keep both eyes open. Read the measurement at the center of your right pupil—this is your binocular PD (total PD for both eyes). Most adult PDs range between 57–74 mm.

Step 4: Double-Check for Accuracy

• Take at least 2–3 measurements to ensure consistency.
• If you have someone available, ask them to measure for you—it’s often easier and more precise.
• If your numbers vary slightly, use the average of your measurements.

Alternative: Measuring Monocular PD (For Each Eye Separately)

Some prescriptions require monocular PD, meaning separate measurements for each eye. If your PD is written as two numbers (e.g., 33/32), this means the distance from the center of your nose to each pupil is slightly different.

How to Measure Monocular PD:

• Align the "0 mm" mark with the center of your nose instead of your left pupil.
• Measure the distance from your nose to the center of your left pupil, then from your nose to the center of your right pupil.
• These two numbers together make up your total PD.

Common Mistakes to Avoid

• Tilting Your Head – Keep your head level to avoid measurement errors.
• Measuring at an Angle – The ruler should be flat against your forehead.
• Using Inches Instead of Millimeters – PD is always measured in mm.
• Squinting or Closing One Eye – Keep both eyes open for the most accurate result.

Need an Easier Way? Use a Mobile App!

If you’re struggling with the manual method, some mobile apps can measure your PD using your phone’s camera. We’ll go over how this works in the next section.

Method 2: Use a Mobile App to Measure Your PD

If measuring your pupillary distance (PD) manually feels difficult, you can use a mobile app to get an accurate reading. Many apps use your phone’s camera to calculate your PD automatically, making the process quick and hassle-free.

How PD Measurement Apps Work

PD measurement apps typically use one of the following methods:

• Face Recognition Technology – The app detects your pupils and calculates the distance automatically.
• Card-Based Calibration – Some apps ask you to hold a standard-sized card (like a credit card) against your forehead to help determine scale.

Most apps will guide you through a few simple steps to get your PD measurement within seconds.

Steps to Measure PD Using an App

1. Download a reputable PD measurement app from the App Store (iOS) or Google Play (Android).
2. Follow the on-screen instructions, which may include positioning your face within a frame or holding a card for scale.
3. Keep your head straight and look directly at the camera while the app scans your eyes.
4. Review the results and ensure they seem consistent with typical PD ranges (57–74 mm for most adults).
5. Take multiple readings if necessary to confirm accuracy.

Recommended Features to Look for in a PD App

Not all PD apps are created equal. When choosing one, look for:

• Good user reviews – Ensure the app has positive ratings and feedback.
• Clear instructions – A step-by-step guide within the app helps avoid errors.
• No excessive permissions – The app should not require unnecessary access to your personal data.
• Compatibility with your device – Some apps work better on certain phone models.

While we don’t endorse specific apps, some commonly used PD measurement tools include:

• Apps from well-known eyewear retailers
• General PD measurement apps on the App Store or Google Play

If you prefer a fast and automated method, using an app may be the best way to measure your PD without a ruler or mirror.

Troubleshooting & Common Questions About PD Measurements

Even with the best methods, measuring your pupillary distance (PD) can sometimes lead to confusion. Below, we address the most common issues and questions to help ensure you get the most accurate measurement.

What If My PD Measurements Vary Each Time?

It's normal for your PD to vary slightly when measuring multiple times. If you get different results, take three measurements and use the average. Having a friend assist or using a mobile app can also improve accuracy.

Does My PD Need to Be Exact?

For most single-vision lenses, a 1–2 mm variation is usually acceptable. However, for progressive or bifocal lenses, an exact measurement is more important to prevent distortion.

What If I Have Two PD Numbers on My Prescription?

Some prescriptions list monocular PD, which means the measurement is provided separately for each eye (e.g., 33/32 mm). This is common when your pupils are not perfectly symmetrical. If your prescription includes monocular PD, provide both numbers when submitting your measurement.

Why Isn’t My PD Listed on My Prescription?

Some opticians do not automatically include PD on prescriptions because it’s considered a fitting measurement rather than a prescription requirement. If you haven’t received it, you can call your optician and request the number, as they likely measured it during your exam.

What Happens If My PD Is Wrong?

An incorrect PD can cause:

• Blurry vision due to incorrect lens alignment
• Eye strain or discomfort if the optical center of the lens doesn’t match your pupils
• Distortion, especially for high prescriptions or progressive lenses

This is why we strongly recommend getting your PD from your optician if possible. If self-measuring, take multiple readings for the best accuracy.

Can My PD Change Over Time?

For adults, PD remains stable and does not change unless there is significant weight loss, aging effects, or an eye condition that alters pupil positioning. For children, PD can change as they grow.

How to Submit Your PD to Faded Days and Complete Your Order

Now that you have your pupillary distance (PD) measurement, the final step is to send it to us so we can complete your prescription glasses. Providing your PD ensures that your lenses are positioned correctly for optimal clarity and comfort.

How to Submit Your PD

Reply to the Email You Received from Faded Days

• Simply respond to the email we sent requesting your PD and include your measurement in your reply.
• If you measured it yourself, we recommend providing the average of multiple readings to ensure accuracy.

What Happens Next?

• Once we receive your PD, we will begin crafting your prescription glasses.
  
• If we have any questions about your PD, we’ll reach out to clarify before proceeding.

Looking for the Right Prescription Eyewear?

If you’re not already a Faded Days customer and just came here for information, feel free to explore our collections. We specialize in high-quality eyewear designed for larger head sizes:

• Prescription glasses for big heads – Designed for a perfect fit and all-day comfort.
• Prescription sunglasses frames for large heads – Get UV protection with customized prescription lenses.
• Polarized prescription large sunglasses – Reduce glare while maintaining crystal-clear vision.

Need Assistance?

If you have any trouble measuring your PD or have questions about the process, don’t hesitate to reach out. We’re happy to help ensure you get the best possible fit for your new glasses.