How to Measure Your Pupillary Distance (PD) at Home
PD decides where the optical centre of each lens sits. Get it wrong by three millimetres on a strong prescription and you will feel it as eye strain within the hour.
Pupillary distance is the gap in millimetres between the centres of your two pupils. The lab uses it to place the optical centre of each lens exactly in front of each eye. If the centres are off, you are effectively looking through the edge of the lens — which introduces a small prism effect your eyes then have to fight all day.
Method: ruler and mirror
- Stand about 20 cm from a mirror, in good light, with your head level.
- Hold a millimetre ruler flat against your brow, just above your eyes.
- Close your right eye. With your left eye, line the ruler's zero mark up with the centre of your left pupil.
- Without moving the ruler, close your left eye and open your right. Read the millimetre mark that now sits over the centre of your right pupil.
- That number is your distance PD. Repeat it three times and take the value you got most often.
Single PD vs dual PD
A single PD is one number, such as 63. A dual PD is two, such as 31.5 / 31.5, measured from the centre of the nose to each pupil separately. Faces are rarely perfectly symmetrical, so dual PD is more precise — and it is what progressive lenses and strong prescriptions really need.
Near PD
Your eyes converge slightly when reading, so the near PD is about 3 mm smaller than the distance PD. If you are ordering reading glasses only, subtract 3 from your distance measurement.
When a home measurement is not enough
- Progressive or bifocal lenses — these also need the fitting height measured on the chosen frame, which cannot be done at home.
- A prescription stronger than about ±4.00, where a 2 mm error becomes noticeable.
- Any prism correction in the prescription.
- Children's glasses — always have these measured professionally.
It takes under a minute at any branch, and we will write it down for you whether or not you buy that day.
Have it measured in storeFrequently asked questions
What is the average pupillary distance?
Around 63 mm for adult men and 61 mm for adult women, with a normal range of roughly 54 to 74 mm. Children measure lower, typically 43 to 58 mm. These averages are only a sanity check — always use your own measurement.
Can I measure my PD from a photo?
You can, using a card of known width such as a bank card held against your forehead as a scale reference. It is less reliable than a ruler because camera angle and lens distortion both shift the result, so treat it as an estimate and verify it against the ruler method.
Does my PD change over time?
Not in adults — it is set once the skull stops growing. In children it increases as they grow, which is one of the reasons children's glasses need remeasuring each year.