PD, or pupillary distance, is the distance in millimeters between the centers of your two pupils. For adults, the normal range falls between 54 and 68 mm, though measurements anywhere from 48 to 73 mm are considered acceptable. You need this number when ordering glasses because it tells the lab exactly where to position the optical center of each lens in front of your eyes.
Average PD for Adults
Adult men tend to have a wider PD than women. Among men in large population studies, the range runs from about 55 mm at the lower end to 70 mm at the upper end. For women, the typical spread is 53 to 65 mm. Most people land somewhere in the low-to-mid 60s, which is why many ready-made reading glasses are manufactured with a PD of 62 or 63 mm.
Children have noticeably smaller PDs, often in the low 40s to mid-50s, and the measurement gradually increases as the face grows. By the late teens, PD is usually close to its adult value and stays relatively stable from there.
Binocular PD vs. Monocular PD
Your PD can be recorded two ways. A binocular PD is a single number (for example, 63 mm) measuring the full distance from one pupil to the other. A monocular PD splits that into two numbers (for example, 31/32 mm), measuring from the bridge of your nose to each pupil separately.
Most faces are not perfectly symmetrical, so your left and right monocular PDs may differ by a millimeter or two. For basic single-vision lenses, a binocular PD works fine. Monocular PD becomes more important with progressive lenses or bifocals, where each lens has distinct viewing zones that need to be aligned precisely with each eye.
Distance PD vs. Near PD
When you look at something far away, your eyes aim nearly parallel and your PD is at its widest. When you focus on something close, like a book, your eyes converge inward and the effective distance between your pupils shrinks. This smaller measurement is your near PD.
The rule of thumb is simple: subtract 3 mm from your distance PD to get your near PD. If your distance PD is 63 mm, your near PD is 60 mm. For monocular measurements, subtract 1.5 mm from each side. So a dual PD of 33/31 becomes 31.5/29.5 for reading glasses. If you’re ordering glasses specifically for reading or close-up work, using the near PD keeps the optical centers aligned with where your eyes actually point at that distance.
Why an Incorrect PD Causes Problems
When your PD is off, the optical center of each lens no longer lines up with your pupil. Your eyes are forced to look through an off-center portion of the lens, which bends light at a slight angle. This creates an unintended prism effect that makes your eye muscles work harder to fuse the images from both eyes into one.
The most common symptoms are eyestrain, headaches, and blurry or slightly distorted vision. How bad these feel depends largely on your prescription strength. A 2 mm PD error in a mild prescription might cause only faint discomfort you can adapt to. The same 2 mm error in a strong prescription produces significantly more unwanted prism, and symptoms can be immediate and hard to ignore. The relationship is linear: double the lens power, double the prism from the same amount of misalignment.
How Much Error Is Allowed
The U.S. optical industry follows the ANSI Z80.1 standard, which sets specific tolerances for how far off the lens centers can be from your specified PD. For single-vision lenses with a prescription of ±2.75 diopters or less, the standard permits a small amount of prismatic imbalance (about two-thirds of a prism diopter between the two lenses). For stronger prescriptions, the lenses must be placed within ±2.5 mm of your specified PD.
Progressive lenses are held to a tighter standard. Each lens must be mounted within ±1.0 mm of your specified monocular PD. That’s because progressives have narrow corridors for intermediate and near vision, and even small horizontal misalignment can push you outside those corridors and create noticeable blur.
How PD Is Measured
The most accurate method is a pupillometer, a handheld device your optician or optometrist looks through while you focus on a target light. It gives a reading precise to about half a millimeter and can measure each eye independently.
You can also measure PD at home using a millimeter ruler and a mirror. Stand about arm’s length from the mirror, hold the ruler across your brow, close your right eye, and align the zero mark with the center of your left pupil. Then, without moving the ruler, close your left eye and open your right, reading the millimeter mark that falls on the center of your right pupil. That number is your binocular PD. Repeating the process a few times and averaging the results improves accuracy.
Several online retailers and apps now offer PD measurement tools that use your phone camera and a reference object like a credit card. These can get you in the right ballpark, but they’re generally less precise than a pupillometer. For a mild single-vision prescription, being off by a millimeter is unlikely to cause noticeable issues. For progressive lenses or strong prescriptions, it’s worth getting a professional measurement.
What to Do if Your PD Isn’t on Your Prescription
In most states, PD is not legally required to appear on your eyeglass prescription. Many eye care offices measure it but record it in your fitting notes rather than on the prescription form itself. If you’re ordering glasses online and don’t see a PD on your paperwork, you can call the office that did your exam and ask for it. They should have it on file. Alternatively, any optical shop can measure your PD in a few seconds, often at no charge, even if you’re not buying glasses there.