How to measure your pupillary distance

You’ve got your prescription, you’ve chosen your frame… but then you need a small but important detail: your pupillary distance (PD).

It’s one of those measurements that sounds technical, but in reality, it’s super straightforward to attain at home.

Once you have this measurement, your PD ensures your lenses are centred exactly where your eyes look through them. Get it right, and everything feels sharp, comfortable, and effortless. 

The good news? You don’t need fancy equipment or an awkward conversation with your optician. In just a few minutes, you can measure your PD accurately yourself.

Free PD Ruler

To make things as simple (and accurate) as possible, you can download this free printable PD ruler you can use at home. Click here to download your free PD ruler and get started straight away.

 

What is Pupillary Distance?

Pupillary Distance (PD) is the measurement, in millimetres, between the centres of your pupils.

It’s used to position your prescription lenses so that your eyes look through the optical centre of each lens. This alignment is what gives you clear, comfortable vision.

Without an accurate PD, even a perfectly made prescription can feel slightly blurred or strained.

 

Types of Pupillary Distance

Single PD also know as Binocular PD, is one total measurement across both eyes. For example, 64mm.

This is most commonly used for single vision lenses and is generally suitable for lower-strength prescriptions where a small margin of error is less noticeable.

Dual PD also known as monocular PD, splits the measurement into two numbers—one for each eye. For example:

• Right eye (OD): 32mm
• Left eye (OS): 32mm

This method is more precise and is especially important for varifocal lenses or stronger prescriptions, where accurate lens positioning is critical.

 

How to Measure Pupillary Distance at Home

Measuring your PD at home is simple and only takes a few minutes. Below are a few reliable methods you can use depending on what you have available.

 

Before you start

Before measuring anything yourself, it’s worth checking your prescription. Occasionally, some optician's include your PD on your prescription paper, often tucked away or printed on the reverse side.

• A single number (e.g. 64mm) indicates your total PD
• Two numbers (e.g. 32 / 32) indicate dual PD

If it’s there, you’re all set. If not, proceed to the various methods listed below.

 

Method 1: Using Our Free PD Ruler

We’ve designed a printable PD ruler to make measuring your pupillary distance easier and more accurate—especially if you’re doing this on your own.

Steps:

1. Print this sheet to “actual size.”
2. Fold along the centre line which intersects the ruler.
3. With scissors, cut-out the three grey boxes.
4. Locate the V slot over your nose.
5. Keep the paper taut and straight.
6. Measure the distance between each of your pupils.

Pro tips:

Take a few measurements and compare results
For single vision lenses, you can safely average your results
For varifocals, use dual (monocular) PD measurements for greater accuracy

Method 2: Using a Regular Ruler

You can measure your PD with a standard ruler, although it can be slightly fiddly to keep steady.

Steps:

1. Hold the ruler across your brow, just above your eyes
2. Make sure the millimetre scale is facing downward
3. Close your right eye and align the 0mm mark with the centre of your left pupil
4. Look straight ahead
5. Close your left eye and open your right
6. Note the measurement at the centre of your right pupil

That number is your total PD.

 

Method 3: Using an Old Pair of Glasses

A simple and surprisingly effective method... with a little help from someone else.

Steps:

1. Put on your existing glasses
2. Ask a friend to mark the centre of each pupil on the lenses using a non-permanent marker
3. Remove the glasses
4. Measure the distance between the two dots

That measurement is your PD.

 

Method 4: Using a Mobile App

If you don’t have a ruler or printer to hand, a pupillary distance app can be a quick and convenient alternative.

Below are some of the best options available on both iPhone and Android. Each one uses your phone’s camera to estimate your PD in just a few seconds.

PD+ (Pupillary Distance) Free (with optional upgrades) Simple, accurate, and easy to use. One of the best standalone PD apps without ties to eyewear retailers.

Eye Measure Paid. Uses your phone’s camera and a reference card (like a bank card) to deliver highly accurate measurements.

 

A Quick Note on Accuracy

PD apps are a great tool when you’re in a pinch, but they’re not always perfect.

Lighting, camera quality, and positioning can all affect the result. If you’re ordering varifocals or have a stronger prescription, it’s worth double-checking your measurement using a ruler or our printable PD tool.

 

How Important is PD for Glasses?

Your PD plays a key role in how your glasses perform. It ensures your eyes are aligned with the optical centre of each lens, which directly affects visual clarity and comfort.

For mild single vision correction, there can a bit more tolerance. But for varifocal lenses (progressives) or stronger prescriptions, even small inaccuracies can lead to distortion, eye strain, or difficulty focusing.

In short, it’s a small measurement that makes a big difference.

 

What If Your Pupillary Distance Has Two Numbers?

If your prescription lists two PD values, these are your monocular (dual) measurements—one for each eye.

For single vision lenses, these can be added together to give a total PD if required.

However, for varifocal or more complex prescriptions, dual PD is essential. It allows each lens to be positioned precisely in front of each eye, improving clarity across all viewing zones.

If you’re measuring at home, we recommend capturing each eye individually using a PD ruler for the best result.

 

My Mono PDs Are Slightly Different?

That’s completely normal. Most people have a slightly asymmetrical face, so it’s common for each eye to have a slightly different measurement.

For example:
Right eye: 31mm
Left eye: 33mm

This small variation is expected and nothing to worry about.

 

What is the Average PD?

If you’re ordering single vision lenses, using an average PD can sometimes work, but it’s not ideal. Average doesn’t mean accurate. If you can, it’s always worth taking a few minutes to measure your own PD properly.

Typical averages:

• Men: around 64mm
• Women: around 62mm

Most adult PDs fall somewhere between 58mm and 73mm.

 

Frequently Asked Questions

How Are Mono and Dual Pupillary Distances Written on a Prescription?

A single PD is written as one number in millimetres. A dual PD is written as two separate numbers—one for each eye. These may be labelled as Right and Left, or as OD (right eye) and OS (left eye).

 

Do You Need PD for Sunglasses?

Your PD is important for all prescription eyewear, including prescription sunglasses, as it ensures proper lens alignment. However, it is not required for non-prescription sunglasses.

 

Does PD Change Over Time?

PD changes as you grow during childhood. But once you reach adulthood, it remains largely stable and does not significantly change over time. Which is handy, as you can keep a note of your PD on your phone or prescription paper knowing that it won't change.

However, it's worth remembering that whilst your adult PD will never change, your Ocular Height will vary from glasses frame to glasses frame. To learn more about ocular height and how to measure it check out this handy blog post.

Thanks for reading.