Disclaimer: We recommend getting the same prescription power as your current glasses as it is the most accurate. Prescription power obtained from an autorefractor can be inaccurate and might cause vision problems and discomfort if used.
How to measure PD
Stand about 30cm away from a mirror.
Looking at yourself, hold a ruler up against your eyebrows.
Close your left eye, then line up the ruler so that 0mm is in line with the middle of your left pupil.
Then close your right eye and line up the ruler again. Your PD is the figure aligned with the center of your left pupil.