Pupillary distance is short for PD. It is the distance between the center of your two pupils in millimeters. Your eye care provider will usually measure your PD during an eye exam. 

Eye care providers usually list the PD when filling out a prescription for you. If it's not there, you can still measure it on your own. Prepare yourself a mirror, a millimeter ruler, and follow the steps below.

Step 1: Stand 8 inches (20 cm) away from the mirror.

Step 2: Hold the ruler against your eyebrows, with your face straight.

Step 3: Close your right eye and align the ruler's 0 mm to the center of your left pupil.

Step 4: Look straight. Close your left eye and open your right one.

Step 5: Read the mm line that lines up with the center of your right pupil. This number is your PD.

Note: 
• Repeat three times for accuracy

• Range of Adult PD: 54-74 mm

• Range of Child PD: 43-58 mm

• A measurement error of about 2mm is acceptable