Stand in front of a mirror
Hold a ruler in millimeters against your brow
Close your right eye
Align the ruler’s zero with the center of your left pupil
Open your right eye and close your left eye
Read the measurement at the center of your right pupil
Repeat the measurement 2 to 3 times
Use the average of the readings as your PD
For near PD, measure while looking at a point about 40 cm away
For distance PD, measure while looking at a far object
Ask another person to help if needed
Record the result in millimeters
Measure in good lighting
Keep your head straight and eyes level