Pupillary distance (PD) is one of the most important measurements for ordering prescription glasses online. This guide shows you a quick, accurate way to measure PD at home, explains dual PD (monocular PD), and answers the most common questions people ask about PD measurements.
1) What is Pupillary Distance (PD)?
Pupillary distance (PD) is the distance (in millimetres) between the centres of your pupils. Your PD tells the lab where to position the optical centre of each lens so you look through the clearest part of your glasses.If PD is inaccurate, you may notice blurred vision, eye strain, headaches, or a “not quite right” feeling—especially with higher prescriptions.
If you’re ordering glasses online for the first time, our frame size and fit guide helps you choose a comfortable frame before you enter your PD.
2) How to Measure Your PD (Mirror Method)
This mirror method is suitable for most single-vision prescriptions. For progressive or high prescriptions, higher accuracy may be required.
Your optician may measure PD during an eye test, but it isn’t always listed on your prescription. You can measure it yourself at home with a mirror and a millimetre ruler.
What you need
- A millimetre ruler (mm)
- A mirror
- Good lighting
Step-by-step: single PD (distance PD)
- Stand about 20 cm (8 inches) away from a mirror.
- Hold the ruler flat against your brow (just above your eyes).
- Close your right eye. Align 0 mm with the centre of your left pupil.
- Without moving the ruler, look straight ahead. Close your left eye and open your right eye.
- Read the mm mark that lines up with the centre of your right pupil. That number is your PD.
Tip: Keep your head still and avoid tilting the ruler. A small angle can change the result by a few mm.
3) Tips to Get the Most Accurate PD
- Measure 3–4 times and use the most consistent result.
- Measure in mm (not cm).
- Use bright lighting so pupil centres are easier to identify.
- If you wear glasses, measure without them (unless a professional instructed otherwise).
- If results vary a lot, ask a friend to help you measure for better accuracy.
4) Average PD for Adults and Kids
Most adult PD measurements fall within this range, but individual facial structure and prescription needs can vary.These ranges can help you sanity-check your measurement:
- Adults: typically 54–74 mm
- Kids: typically 43–58 mm
If your number is outside these ranges, it doesn’t automatically mean it’s wrong—but remeasure to confirm. For stronger prescriptions or progressive lenses, accuracy matters even more.
5) What Is Dual PD (Monocular PD)?
Dual PD (also called monocular PD) splits the measurement into two numbers: the distance from the bridge of your nose to the centre of each pupil.
It’s written like 32/30:
- 32 = right eye (OD)
- 30 = left eye (OS)
Dual PD can be especially helpful if your pupils are not perfectly centred or your face is slightly asymmetrical (which is normal).
PD Measurement FAQs
Is PD the same as my prescription?
No. Your prescription (SPH/CYL/AXIS) describes lens power. PD is a separate measurement used to position the optical centre of the lenses.
What if my prescription doesn’t include PD?
That’s common. You can measure it at home using the steps above or ask your optician to provide it.
Should I use single PD or dual PD when ordering?
If you have dual PD, use it. If you only have a single PD, that’s also fine for most single-vision lenses. For complex prescriptions or progressives, dual PD is often preferred.
How accurate does PD need to be?
Ideally within 1–2 mm. The higher your prescription, the more important precision becomes for comfort and clarity.