Your interpupillary distance (IPD) is the distance in millimeters between the centers of your two pupils. The average adult IPD is about 63 mm, but it ranges widely from 50 mm to 70 mm, with some people falling anywhere from 45 mm to 80 mm. You need this number to order glasses online, set up a VR headset, or verify that your prescription eyewear is properly centered.
The Mirror and Ruler Method
This is the most common DIY approach and requires only a millimeter ruler and a mirror. Stand about 8 inches from the mirror and look straight ahead. Hold the ruler flat against your brow line so it doesn’t slip. Close your right eye and align the ruler’s 0 mm mark with the center of your left pupil. Then, keeping the ruler perfectly still, open your right eye and close your left. The millimeter mark that lines up with the center of your right pupil is your IPD.
The tricky part is keeping the ruler steady while switching eyes. If the ruler shifts even slightly, you can be off by a couple of millimeters. Run the measurement three times and use the number that comes up most often. If you get three different readings, take the middle value.
Having Someone Else Measure You
A second person with steady hands can get a more reliable reading because the process eliminates the awkward eye-switching step. Sit facing your partner at eye level, roughly arm’s length apart. Look at something in the distance behind them (not at their face) so your eyes stay relaxed and parallel. Your partner holds the ruler across your brow and reads the distance from the center of one pupil to the center of the other.
Looking at a distant object matters because it keeps your eyes from converging inward the way they do when focusing on something close. Even a slight inward turn can shrink your reading by 1 to 2 mm. For the same reason, make sure your partner lines up each measurement from directly in front of you, not from an angle.
Smartphone Apps
Several free apps can estimate your IPD using your phone’s front camera. A study comparing three popular options found that the Warby Parker and EyeMeasure apps were the most accurate, averaging less than about 0.5 mm off from a professional digital pupillometer. The PDCheck AR app was significantly less accurate, averaging closer to 1.4 mm off. The Warby Parker app walks you through the process, asking you to hold the phone at arm’s length and follow an animated circle, and it prompts you to remove glasses or adjust your head position. Other apps offer less guidance, which tends to produce less consistent results.
If you go the app route, good lighting and a steady hand make a real difference. Take several readings and compare them. If the numbers cluster within 1 mm of each other, you can feel confident in the result.
How Accurate You Actually Need to Be
For standard single-vision glasses, industry tolerances allow up to 2.5 mm of offset from your specified IPD before the lens creates noticeable prismatic distortion. Progressive lenses are stricter: fitting crosses need to land within 1.0 mm of your monocular IPD. So if you’re ordering basic reading glasses or distance glasses online, being off by 1 mm is fine. If you’re ordering progressives or have a strong prescription, precision matters more, and a professional measurement is worth the effort.
A home measurement within 1 mm of your true IPD is realistic with careful technique. That’s accurate enough for most single-vision orders and for dialing in a VR headset.
Binocular vs. Monocular IPD
Most online glasses retailers ask for a single number, your binocular IPD, which is the total distance from one pupil center to the other. But your face probably isn’t perfectly symmetrical. Monocular PD splits the measurement into two numbers: the distance from the bridge of your nose to each pupil separately. You might be 31 mm on the left and 33 mm on the right, for example, giving you a binocular total of 64 mm.
Monocular measurements are recommended for progressive lenses, prism prescriptions, higher-index lenses, and anyone with noticeable facial asymmetry. If you need monocular PD, the partner method works well. Have them measure from the center of each pupil to the center of the bridge of your nose, one eye at a time.
Getting a Professional Measurement
Any optometrist or optician can measure your IPD in seconds using a pupillometer, a handheld device you look into while the clinician reads the display. Automated pupillometers are more consistent than manual methods and suffer from less variability between different examiners. If you already have a recent glasses prescription, your IPD may be written on it, though not all providers include it automatically. You can call and ask.
Some optical shops will measure your IPD for free even if you don’t buy glasses from them, though policies vary. It’s the fastest way to get a number you can trust for progressive lenses or a strong prescription.
Why IPD Matters for VR Headsets
Most VR headsets have either a physical IPD adjustment dial or a software setting. When the distance between the headset’s lenses doesn’t match your IPD, you may notice blurry edges, eye strain, or a sense that the 3D depth looks “off.” Research on VR gameplay found that a mismatch of 6 to 10 mm caused measurably higher rates of problems with focusing and eye convergence compared to smaller misalignments. Even a moderate mismatch can leave your eyes working harder to fuse the two images, leading to fatigue during longer sessions.
If your headset lets you adjust in 1 mm increments, use your measured IPD as a starting point, then nudge it up or down by a millimeter until the image looks sharpest at the center and edges. Your subjective comfort is the final test.