What is PD number? I never wore eyeglasses before as I have a weak prescription. Now I want to buy a pair of prescription glasses from the online stores, PD number is required. What is PD number? Where can get this PD information? Thanks for your kind help.

Pupillary Distance (PD) is the distance (usually measured in millimeters) between the centers of the pupils in each eye. This measurement is used when assembling prescription eyeglasses. Positioning lenses correctly in relation to the pupil centers is especially important.