Single PD vs. Dual PD: What’s the Difference?

What Is Pupillary Distance?

Pupillary distance, or PD, is the measurement in millimeters used to align the optical center of each lens with your pupils. Accurate PD helps you look through the intended part of the lens.

Single PD

Single PD is one total measurement from the center of one pupil to the center of the other. It often appears as a number such as 63 mm. When an order form requests one PD value, enter the single PD exactly as provided.

Dual PD

Dual PD contains two measurements: the distance from the center of the nose to each pupil. It may appear as 31/32 or as separate right and left values. The two numbers do not need to be identical because faces are not perfectly symmetrical.

Can You Convert Between Them?

Adding the two dual-PD values gives the approximate single PD. Dividing a single PD in half only creates an estimate and may hide natural asymmetry, so use the original dual measurement whenever it is available.

Distance PD and Near PD

Distance PD is generally used for glasses focused on distance vision. Near PD can be smaller because the eyes turn inward when focusing close up. Progressive and multifocal orders may require additional measurements, so follow the lens instructions or ask an eye care professional.

How to Avoid Errors

Measure more than once, keep the ruler level, look straight ahead, and record values in millimeters. If repeated results vary, ask an optician or eye care professional to confirm the measurement before ordering high-prescription or multifocal lenses.