How to measure your pupillary distance (PD)

Your PD is the distance in millimetres between the centres of your pupils. It is needed to place the optical centre of each lens in front of your eye.

Check your prescription first

Many prescriptions already show the PD, sometimes as two numbers (one per eye), e.g. 31.5 / 32.

Measure it with a ruler and a mirror

1. Stand about 20 cm from a mirror in good light.
2. Hold a millimetre ruler flat against your brow, just above your eyes.
3. Close your right eye and line up the zero with the centre of your left pupil.
4. Close your left eye and open your right eye. Read the number at the centre of your right pupil.
5. Repeat three times and use the average. Most adults measure between 54 and 74 mm.

Ask someone to help

Look at a distant object while a friend measures between the centres of your pupils. For reading glasses, look at something about 40 cm away instead (near PD).