Pupillary Distance (PD) is the distance between the center of one pupil to the center of the other pupil, measured in millimeters. Your PD values can be written as one number (known as Binocular PD) if the left and right side have been added together or two numbers (known as Monocular PD) if they are different. E.g. 65 or 32/33
Adding the two Monocular PD values together will always equal the Binocular PD. However, Monocular PD values cannot be reliably achieved by dividing the Binocular PD in half. Faces are rarely perfectly symmetrical, and it is common for one eye to be further from the nose bridge than the other. Because Monocular PD values are more precise, they are required for Progressive and Bifocal lenses.
Why Pupillary Distance (PD) measurement is so important is that every eyeglasses prescription has an optical center. The optical center of your eyeglass lenses is the part that gives you the best vision, and it should be directly in front of your pupils. So how to tell where is the optical center that is specifically for you, that's customized for your eyes? That's when your PD comes in place and your eyeglasses laboratory would need to know it.
So how to measure your PD? Now it's easier than ever! Simply use our 3D Try On feature, real time! You get your PD measurement right away, any day, any time. This is a special feature Glasses Gallery innovatively created for you. We'd like to furnish your optical needs with our state-of-the-art technology, from PD measurement to frames picking, you can count on us to give you the best support.
However, if you like to measure it manually, the most common way is shown below.
Remember you always need to keep your ruler steady and parallel to the floor using this method. If you have a friend to help, this will be much easier. You only need to stand still and let your friend do the measurement.
There's another PD measurement method which is claimed to be very accurate. Posted here also for your reference: