How to measure pupillary distance (PD)

Pupillary distance (PD) is the distance between the centres of your pupils (the black bits in the middle of the eyes). Your PD is an important measurement when your glasses are being manufactured, to make sure you're looking through the best spot in your lenses for clear vision.

If you don't have a copy of an accurate PD measurement from your optician, you could try to measure this yourself, or have a friend help you out.

Measuring your own pupillary distance
1.  Stand about 30cm away from a mirror 
2.  Looking at yourself, hold a ruler up against your eyebrows 
3.  Close your right eye, then line up the ruler so that 0mm is in line with the middle your left pupil 
4.  Look straight ahead again and then open your right eye and close your left 
5.  Your pupillary distance measurement will be the figure that lines up with the centre of your right pupil
 
For reading glasses
Follow the same method but take away 2mm from the distance number. So, if your measurement is 60mm, then your PD for reading glasses will be 58mm.
 
Measuring a friend’s pupillary distance
To measure someone else’s PD, have them look at something around 20 feet away from them with both their eyes open. Using a ruler, line up the 0mm mark with the centre of one pupil, then measure to the centre of the other. You just need to make sure that you stay out of their line of sight, they keep looking straight ahead with their eyes as still as possible, and that they don’t look at you while you’re measuring. Do this a few times to make sure the measurement you get is consistent. The average pupillary distance for adults is usually between 54-74mm.

Extract taken from https://www.specsavers.co.uk/glasses/buyers-guide/how-to-measure-your-pupillary-distance