What is pupillary distance (PD)?

Pupillary Distance (PD) measures the horizontal distance between the centre of your left and right pupils. This measurement determines the point where you look through the lens of your glasses. Pupillary distance ensures optimal clarity of vision.

Knowing your pupillary distance is crucial when it comes to buying a new pair of glasses online. It is particularly essential if you require a strong prescription or varifocals as it won't be an option to use an average measurement for these lenses.

What is PD measured in?

A millimetre ruler or a PD ruler measures pupillary distance. The measurement is in millimetres. It is most often recorded as one value (e.g. 66mm) but can also be written as 33/33 or 34/32 depending on whether you are symmetrical.

Single PD or dual PD

Single PD and Dual PD are methods for measuring pupillary distance.

Single PD, also referred to as binocular PD is the measurement between the centre of one pupil to the other.

Dual PD, also known as monocular PD, measures the bridge of your nose to each eye. This method is the most accurate of the two.

How do I know my pupillary distance?

You can ask your ophthalmic practitioner or optometrist for an accurate PD measurement after your eye exam. Usually, opticians do not give out your PD measurement as the law does not require them to give it to you. Some opticians may even charge you for dispensing your PD information.

Your dispensing optician should ensure that your glasses fit correctly and that the pupillary distance on your lenses is correct.

If you don't know your pupillary distance, you can measure it yourself at home with the help of a friend or the mirror.

How to measure your pupillary distance?

With a mirror

• Standing 8 inches away from a mirror, hold a ruler against your eyebrow.
• Close your right eye and align the ruler's 0mm with the centre of your left pupil. The millimetre scale should be pointing upwards.
• Look straight ahead and shut your left eye while keeping your right eye open.
• Your pupillary distance will be the millimetre line that lines up to the centre of your right pupil.

With a friend

• Focus on something 20 feet away from you.
• Have your friend positioned just outside your peripheral vision at roughly the same height as you and get them to hold the ruler across your brow.
• Ask them to line up the ruler's zero to your right pupil and measure across to your left pupil.

How to measure pupillary distance using old glasses

• Keep your focus on an object 20 feet away.
• Mark a dot on your left and right lenses, where the object appears.
• Measure the distance between both the marker dots using a millimeter ruler. Your PD is the distance between these dots.

How do you calculate near PD for reading glasses?

To calculate your near PD, subtract 3mm from your distance PD.

If you are calculating your near PD using you dual PD, you will only need to subtract 1.5mm from each eye's measurement.

What is the average PD?

A PD measurement between 58-68 is considered normal for men and women. The average pupillary distance for a man is 64mm and for women 62mm. For this reason we have set our default PD measurement at 63mm.

What happens if PD is wrong on glasses?

If the pupillary distance is wrong on your glasses, this can result in eye strain, fatigue and blurry vision. A high prescription with the wrong PD can make these symptoms much worse. The wrong PD won't damage your eyesight; however, it will certainly be noticeable.

Do you need PD for glasses?

Pupillary distance PD is necessary for glasses as it determines the optical centre in the prescription lenses. The optical centre is where you look through the lens of your glasses.