How To Measure Your PD
How to Measure Your Pupillary Distance (PD) for Glasses ๐
If you've ever tried to order glasses online and hit a wall when asked for your PD โ you're not alone. Pupillary distance is one of the most commonly misunderstood measurements in eyewear, and many South African optometrists don't automatically include it on your prescription.
The good news: measuring your PD at home is straightforward, takes less than two minutes, and doesn't require any specialist equipment. This guide covers everything you need to know.
๐๏ธ What Is Pupillary Distance (PD)?
Pupillary distance โ usually abbreviated as PD โ is the measurement in millimetres between the centre of your right pupil and the centre of your left pupil. It sounds simple, but it's one of the most important measurements in prescription eyewear.
When your lenses are made, the optical centre of each lens needs to align precisely with your pupil. If the PD is even slightly off, your eyes have to work harder to compensate โ which can cause headaches, eye strain, blurry vision, and general discomfort, even if your prescription itself is perfectly correct.
In short: a wrong PD can ruin an otherwise perfect pair of glasses.
๐ข Single PD vs Dual PD โ What's the Difference?
You may see two types of PD on your prescription:
One measurement representing the total distance between both pupils โ for example, 64mm. This is the most common format and what most online optical stores use.
Two separate measurements โ one for each eye. For example: 32mm / 32mm (right / left). Used when a person's eyes are not perfectly symmetrical, which is actually more common than you'd think. If your prescription shows dual PD values, use both โ the more precise the measurement, the better the result.
If your prescription only shows a single PD, that's perfectly fine for most prescriptions.
๐ What Is a Normal PD Measurement?
Adult PD measurements typically fall in the following ranges:
| Group | Typical PD Range | Average |
|---|---|---|
| Women | 57โ65mm | ~62mm |
| Men | 60โ68mm | ~64mm |
| Children | 41โ55mm | Varies by age |
If your measurement falls outside these ranges, don't panic โ individual variation is normal. What matters is accuracy, not where you fall in the range.
โ What If My Optometrist Didn't Include My PD?
This is very common in South Africa. Optometrists are required to give you a copy of your prescription, but PD is sometimes omitted โ particularly if the optometrist assumes you'll be buying glasses from them directly.
If your prescription doesn't include your PD, you have three options:
- Call your optometrist and ask them to add it โ they measured it during your eye test and should provide it on request
- Visit any optometrist and ask for a PD measurement only โ most will do this quickly at no charge or for a small fee
- Measure it yourself at home using the method below
๐ฅ How to Measure Your PD at Home
You can get an accurate PD measurement at home using just a ruler and a mirror. For even better accuracy, ask a friend to help.
Option 1: Download Our Free PD Ruler
We've created a printable PD ruler specifically for SpecsAreUs customers. Print it at 100% scale โ do not scale or fit to page, as this will affect the accuracy of the measurement.
Option 2: Use a Standard Ruler โ Step by Step
- Stand in front of a mirror in a well-lit room, approximately 20โ30cm away
- Hold a millimetre ruler flat just above your eyes, against your brow
- Close your right eye. Align the zero (0mm) mark with the centre of your left pupil
- Open your right eye and close your left eye โ without moving the ruler
- Read the measurement at the centre of your right pupil. That number is your PD
Repeat the process two or three times to confirm your measurement is consistent. A variation of 1mm between readings is acceptable.
- Keep your gaze straight ahead โ don't look at the ruler directly
- Use a ruler with clear millimetre markings
- Take the measurement in good natural light
- Remove your glasses before measuring
๐ฑ Can I Use an App to Measure My PD?
Several smartphone apps claim to measure PD using your phone's camera. Some work reasonably well for standard prescriptions โ apps like GlassesOn or EyeMeasure use facial recognition to estimate your PD.
However, for high prescriptions (above +/-4.00 SPH) or significant astigmatism, we recommend using a physical ruler or getting your PD measured by an optometrist. With stronger prescriptions, even a 1mm difference matters more.
๐ How to Enter Your PD When Ordering from SpecsAreUs
Once you have your PD, ordering is straightforward. When you select your lenses during checkout, you'll be prompted to enter your prescription details including your PD. Our lens flow system guides you through each field step by step.
If you're unsure about any part of the process, message us on WhatsApp before you order โ we're happy to walk you through it.
Still not sure about your PD? Just message us โ we'll help you get it right before you order. Your perfect pair awaits. โจ
