# Simple IPD Measurement Method

A few days ago I noticed a post on Reddit about how to measure your IPD, or inter-pupillary distance, without going to an optometrist. The method required a pair of binoculars though, which I don’t have readily available, so I figured I would write down a method I’ve had on my mind for quite some time, probably about two years.

First things first, what is IPD useful for? You might have heard it before, but it’s basically a value for putting lenses in front of your eyes that matches your eyes’ position. This could be either for glasses or, in the near future, for a virtual reality headset.

The images below is what I posted to Reddit as a guide, I was planning on doing photos but it got a bit complicated to do alone so I just went ahead and did some really simple illustrations. Programmer-art if you will.

I tried to keep the language simple but it ended up being more text than I expected, that said here is the pure text version below.

1. You need two tools to do this: a mirror and a ruler. It is probably easier if your mirror is mounted to a wall and if your ruler is metric, but those are not really requirements.
2. Stand straight in front of the mirror, hold up the ruler against the surface so it lines up beneath your pupils.
3. Close your right eye and look with your left eye straight into your left pupil. Shift yourself or the ruler so that the start mark of the ruler lines up beneath the center of your left pupil in the mirror.
4. Now switch so your left eye is closed and your right eye is open, without moving yourself or the ruler. Look with your right eye into your right pupil, the center of your pupil should now line up with your IPD on the ruler!

Make a mental note of it or try to shift your focus to see it more exactly, it should be a fairly accurate estimate. It will not be perfect and it can be hard to see, but it gives you the general ballpark.

That’s it!

I eventually came up with this method after seeing my own reflection on my black phone screen, and how the same amount of me fit inside the borders independent of my distance, just like with a mirror. I imagined an app that would let me slide two circles around to match my pupils and that would be able to tell my IPD, I never got started on it though and considering how easily the above method is to do it manually it was probably for the better.

On Reddit I got a few comments that this can be done with a credit card or a ruler hold to your forehead or just as an extra request when going to the optometrist, and while that is true I just couldn’t help sharing what I had come up with :)

Oh, and happy Oculus Rift day for the people lucky enough to receive their headsets today! ;) I haven’t even gotten a shipping confirmation yet so I’ll be keeping tabs on the news feeds instead!