How to measure PD (Pupillary Distance)
What is Pupillary Distance (PD)
Simply put - Pupillary Distance (PD) is the exact measurement, in millimetres (mm), between the center of your pupils. The measurement starts from the center of one pupil and ends at the center of the other pupil.
When you get an eye exam sometimes they will provide the PD measurement right on the eyeglass prescription. However, most eye doctors or optometrists may not provide this information in your prescription.
The average PD measurement for adults is typically between 54mm-74mm. For kids, they can range from 43mm-58mm.
If you don’t have your PD, that’s okay. Measuring your PD is a simple process and can be done with tools you’ll easily find laying around your home.
Why Do We Need PD?
Each pair of prescription eyeglasses or sunglasses have an “optical centre” within the lens. The “optical centre” is the optimal viewing area for correcting your vision and is aligned directly in front of your pupil.
The PD measurement acts as a guide to make sure the lenses have been centred according to the position of your pupils. This will ensure that the lenses are placed in the frame correctly to give you clear and comfortable viewing experience.
How to Measure Your PD | 5 Simple Steps
Things you’ll need
- A ruler with mm increments
- A mirror
- A friend (optional)
Steps
- Stand in front of a mirror or a friend - Stand about 8 inches away from a mirror or your friend
- Ruler on brows - Hold the ruler against your brow line
- Align to zero mm - Close your right eye and align the ruler’s 0mm line with the center of your pupil
- Open right eye and close the left eye - While keeping the ruler’s position secure, open your right eye, and close the left eye.
- Measure PD - Look straight ahead in the mirror and read the millimetre line that is aligned to the center of your right pupil. If you have a friend present, have them measure the distance between the center of your pupils.
The number you get from this measurement is known as your distance Pupillary Distance (PD). Most adults will have a PD measurement of 54mm-74mm.
If you’ve had your PD measured by a licensed professional enter the value as it’s written. Just select single or dual depending on what is written on your prescription, including the decimal values if any (i.e. 61.5).
Single PD VS Dual PD
Single
A single PD or binocular measurement is the overall distance between the centre of the right pupil to the centre of the left pupil.
Dual
A dual PD or monocular PD is made up of two numbers that tell you the distance between the centre of each pupil to the bridge of your nose. The two numbers will correlate the distance for both left and right pupil relative to the bridge of your nose.
Near PD for Reading Glasses
When you’re reading something up close your eyes will converge to the centre to focus on what you’re looking at. This convergence of your pupils will naturally reduce your PD value so a Near PD is needed for reading prescription lenses.
How To Calculate Your Near PD For Reading Glasses
Getting your Near PD measurement is easy with the help of your existing distance PD value. To calculate for Near PD you simply subtract 3mm from your distance PD measurement.
For example, if your distance PD is 62mm, then your near PD will be 59mm
If you’re using dual PD measurements, then you would only subtract 1.5mm from each eyes measurement.
For example, if your dual PD is 32/30 then your dual near PD would be 30.5/28.5