Pupillary distance (PD) is one of the most important measurements for ordering prescription glasses online. This guide from Cinily Glasses explains how to measure PD at home, introduces dual PD (monocular PD), and answers common questions about PD measurements.
Once you have your PD, explore the options in our prescription lens options guide.
1) What Is Pupillary Distance (PD)?
Pupillary distance (PD) is the distance, measured in millimeters, between the centers of your pupils. Your PD tells the lab where to position the optical center of each lens so your prescription lenses align with your eyes.
If your PD is inaccurate, you may notice blurred vision, eye strain, headaches, or a feeling that your glasses are not quite right, especially with stronger prescriptions.
If you’re ordering glasses online for the first time, our frame size and fit guide can help you choose a comfortable frame before you enter your PD.
2) How to Measure Your PD: Mirror Method
This mirror method can be used for many single vision orders. Progressive lenses or stronger prescriptions may require more precise measurements.
Your eye care provider may measure PD during an eye exam or glasses fitting, but it is not always listed on your prescription. You can also measure it at home with a mirror and a millimeter ruler.
What You Need
- A ruler marked in millimeters (mm)
- A mirror
- Good lighting
Step-by-Step: Single PD (Distance PD)
- Stand about 8 inches (20 cm) away from a mirror.
- Hold the ruler flat against your brow, just above your eyes.
- Close your right eye. Align the ruler’s 0 mm mark with the center of your left pupil.
- Without moving the ruler, look straight ahead. Close your left eye and open your right eye.
- Read the millimeter mark that lines up with the center of your right pupil. That number is your single PD.
Tip: Keep your head still and the ruler level. Tilting the ruler or moving your head can change the measurement.
3) Tips for a More Accurate PD Measurement
- Measure three or four times to check that your results are consistent.
- Record your measurement in millimeters, not centimeters.
- Use good lighting so the centers of your pupils are easier to identify.
- Measure without your glasses unless your eye care provider has instructed you otherwise.
- If your results vary significantly, ask someone to help or have your eye care provider confirm the measurement.
4) PD Reference Ranges for Adults and Children
PD varies from person to person. The following ranges provide a general reference when checking your measurement:
- Adults: typically 54–74 mm
- Children: typically 43–58 mm
If your measurement falls outside these ranges, it does not automatically mean it is incorrect. Measure again to confirm your result. For stronger prescriptions or progressive lenses, accurate measurements are especially important.
5) What Is Dual PD (Monocular PD)?
Dual PD, also called monocular PD, records two separate measurements: the distance from the center of the bridge of your nose to the center of each pupil.
For example, dual PD may be recorded as R 32 mm / L 30 mm:
- Right eye (R / OD): 32 mm
- Left eye (L / OS): 30 mm
Dual PD accounts for differences between the right and left measurements, which can occur when the face is slightly asymmetrical. Keep the right and left labels with your measurements when submitting your order.
PD Measurement FAQs
Is PD the same as my prescription?
No. Your prescription values, such as SPH, CYL, and AXIS, describe your lens correction. PD is a separate measurement used to position the optical center of each lens.
What if my prescription doesn’t include PD?
PD is not always listed on an eyeglass prescription. You can ask your eye care provider for the measurement or use the mirror and millimeter ruler method described above.
Should I use single PD or dual PD when ordering?
If you have dual PD, provide both measurements and clearly label the right and left eyes. Single PD can be used for many single vision orders. For progressive lenses or complex prescriptions, dual PD is often preferred.
How accurate does PD need to be?
Aim for the most precise measurement possible. Stronger prescriptions generally require greater precision for comfort and clarity. Repeat your measurement several times and ask your eye care provider to confirm it if the results are inconsistent.