What is IPD?
Interpupillary distance (IPD) is the distance between the centers of a user's pupils, usually measured in millimeters. Adult IPD typically ranges from about 54 to 78 millimeters and averages around 63 millimeters, and matching a headset's lenses to this measurement is critical for accurate scale perception and comfortable stereoscopic viewing.
How does IPD work?
IPD varies significantly between individuals, and it directly affects how a user perceives scale, depth, and comfort inside a headset.
Each lens in a headset has its own optical center; when a user's pupils don't line up with those centers, the images shown to each eye no longer match how the brain expects binocular vision to work.
This mismatch is what causes visual discomfort, eye strain, and incorrect scale perception, and the risk grows once a game or app targets multiple headset platforms that support different fixed or adjustable IPD ranges.
How is IPD used?
Most modern headsets support IPD adjustment in one of two ways:
- Physical adjustment: A slider or dial that physically moves the lenses.
- Software-based adjustment: Rendering each eye's view from a virtual camera separation that matches the user's IPD, without moving any hardware.
For developers building XR titles in Unity, this means reading the user's IPD wherever the platform SDK reports it, then using that value to set stereo camera separation rather than assuming a fixed average. Testing across the real adult IPD range, not just the average, helps catch scale and comfort problems before a title ships across multiple headset platforms.
Frequently asked questions (FAQ)
How do I measure my own IPD?
You can estimate your IPD with a millimeter ruler and a mirror by measuring the distance between the centers of your pupils while looking straight ahead, or use a smartphone app that calculates it from a selfie. An optician can also measure it precisely, since IPD is the same measurement used to fit eyeglass lenses.
Do all VR and AR headsets support IPD adjustment?
No. Most mainstream standalone and PC headsets offer physical or software IPD adjustment, but some budget and mobile-insert headsets ship with a single fixed IPD or only a few preset positions, which can leave part of the adult population with a poor fit.
Can a mismatched IPD cause motion sickness?
Not directly. A mismatched IPD mainly causes eye strain, visual discomfort, and incorrect scale perception. But those symptoms can compound with other triggers, like low frame rates or high latency, and make cybersickness set in faster or feel worse.