What Is Pupillary Distance (PD)?
Pupillary Distance (PD) is the measurement (in millimetres) between the centres of your pupils. It’s a critical value used when crafting prescription glasses to ensure your lenses are properly aligned with your eyes.
Getting this measurement right ensures that you’re looking through the optical centre of each lens — which is essential for clear, accurate vision.
Why Is PD Important?
Your PD ensures your lenses are fitted to match the natural positioning of your eyes. If it’s off, even by a few millimetres, it can cause:
Eye strain
Headaches
Distorted or blurred vision
It’s especially important if:
You wear varifocal or bifocal lenses
You have a high prescription
You experience discomfort with existing glasses
How to Measure Your PD at Home
You can measure your PD yourself with a few simple tools and a mirror. Here’s how:
What You’ll Need
A millimetre ruler or PD ruler
A mirror
Good lighting
📏 Steps to Measure PD
Stand in front of a mirror, keeping your head straight and level.
Hold the ruler flat against your brow, just above your eyes.
Close your right eye, and align the 0 mm mark of the ruler with the centre of your left pupil.
Open your right eye and close your left eye, then read the measurement at the centre of your right pupil.
The number you see (typically between 54–74 mm) is your PD.
You may wish to repeat the process a couple of times to ensure accuracy.
Pro Tip:
If you’re struggling, ask a friend or family member to help — or use a digital PD measurement app or printable ruler.
Can I Guess My PD?
No — please don’t guess your PD.
This measurement is too important to estimate, especially if you’re ordering varifocals or have a high prescription.
If it’s not written on your prescription, your optician can usually provide it. Some may charge a small fee, but it’s worth it to get the most accurate glasses.
Final Thoughts
Measuring your PD is a small but essential step to getting the perfect fit for your glasses. With just a ruler and a mirror, you can ensure your lenses are positioned correctly — giving you the sharpest and most comfortable vision possible.
