How to Measure Your PD at Home (Step-by-Step Guide)

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If you’ve ever tried to buy glasses online and hit a wall when asked for your PD, you’re not alone. Pupillary distance – or PD – is one of those measurements that opticians don’t always include on your prescription, but online retailers need it to make your lenses correctly.

The good news? You can measure it yourself at home in under two minutes, with nothing more than a ruler and a mirror. Here’s exactly how to do it.

What Is PD and Why Does It Matter?

Your pupillary distance is the measurement in millimetres between the centres of your pupils. It tells the lens maker exactly where to position the optical centre of each lens so that you’re looking through the right spot.

Get it wrong and your glasses can cause headaches, eye strain, or just feel “off”, even if the prescription itself is correct. Get it right and your glasses will be comfortable and clear from day one.

PD is usually between 55mm and 75mm for adults, with the average being around 63–64mm. It can be given as a single measurement (e.g. 64mm) or as two separate measurements for each eye (e.g. 32/32mm).

Can You Ask Your Optician for Your PD?

Yes, and you should try this first. Under UK law, opticians must give you a copy of your prescription, and whilst PD isn’t always legally required to be included, most opticians will provide it if you ask.

Simply call or email your optician and ask them to add your PD to your prescription. Most will do this without any fuss, and it’s the most accurate measurement you’ll get.

If they won’t provide it, or if you’d rather measure it yourself, here’s how.

What You’ll Need

• A ruler (millimetre scale)
• A mirror
• A friend (optional but helpful)

Method 1: Measuring Your Own PD With a Mirror

This method works well if you don’t have anyone to help you.

Step 1 – Stand about 20cm (8 inches) away from a mirror in a well-lit room. Keep your face straight and look directly at your reflection.

Step 2 – Hold a millimetre ruler flat against your brow, just above your eyes. Position it so the zero is roughly in the centre.

Step 3 – Close your right eye. Line up the zero mark on the ruler with the centre of your LEFT pupil.

Step 4 – Without moving the ruler, open your right eye and close your left eye. Note the millimetre reading at the centre of your RIGHT pupil.

Step 5 – That number is your PD. Measure it three times and take the average to make sure it’s accurate.

Method 2 – Measuring With a Friend

This method tends to be more accurate as it removes the risk of your eyes moving when you switch between them.

Step 1 – Sit down in a well-lit room and look straight ahead at a point in the distance (not at your friend).

Step 2 – Ask your friend to hold a millimetre ruler flat across your brow, just above your eyes.

Step 3 – Your friend closes one eye and lines up the zero mark on the ruler with the centre of your left pupil.

Step 4 – Keeping the ruler still, they then note the millimetre reading at the centre of your right pupil.

Step 5 – That number is your PD. Repeat three times and average the results.

How to Measure a Split PD (Monocular PD)

Some online retailers ask for a split PD, a separate measurement for each eye from the centre of your nose. This is more precise and particularly useful for varifocal lenses.

Step 1 – Position the ruler as above, but this time line up the zero mark with the centre of your nose (the bridge).

Step 2 – Note the measurement to the centre of your right pupil – this is your right PD.

Step 3 – Note the measurement to the centre of your left pupil – this is your left PD.

The two numbers should add up to your total PD. It’s common for them to be slightly different, for example 31/33mm – which is completely normal.

Tips for an Accurate Measurement

• Always measure in good lighting – natural daylight is best
• Keep your head straight and look at a distant point, not at the ruler
• Measure at least three times and take the average
• If measuring yourself in a mirror, make sure you’re looking at your reflection, not at the ruler
• Wear your glasses if you normally do – measure over the top of them

What If My PD Measurement Is Slightly Off?

For single vision lenses, a small margin of error (1–2mm) is usually fine. Most people won’t notice any difference.

For varifocal lenses, accuracy is more important. If you’re buying varifocals online for the first time, it’s worth getting your PD measured professionally – most opticians will do this for free or for a small fee.

Which Retailers Need Your PD?

Online retailers need your PD because they’re making your lenses remotely without being able to fit the glasses to your face. High street retailers like Specsavers and Vision Express measure your PD in store as part of the fitting process, so you don’t need to provide it yourself.

If you’re buying online and don’t have your PD, use GlassesCompared to see which retailers can help you measure it, or which offer home measurement services.

Ready to Buy?

Now you’ve got your PD sorted, you’re ready to buy glasses online with confidence.