Frequently asked questions

Pupillary distance (PD), also called interpupillary distance (IPD), is the measurement in millimeters between the centers of your pupils. It's essential for properly positioning eyeglass lenses so the optical center aligns with your eyes, ensuring clear and comfortable vision.

When ordering glasses online, you need your PD to ensure the lenses are centered correctly. An incorrect PD can cause eye strain, headaches, and blurry vision. Many eye doctors don't include PD on prescriptions, so you may need to measure it yourself.

Single PD is the total distance between both pupils. Dual PD measures each eye separately from the center of your nose (e.g., Right: 31mm, Left: 32mm). PupiMetric measures single (total) pupillary distance, which is suitable for the vast majority of single-vision glasses and VR headsets. We do not currently provide separate left and right measurements. If your glasses retailer requires dual PD, you can generally divide your total PD by 2 (e.g., a total PD of 62mm becomes 31mm for each eye). About 9 out of 10 people have a left PD and right PD that differ by less than 2 mm, which makes this approximation perfectly acceptable for most people. However, if you have noticeable facial asymmetry or require high-power progressive lenses, an in-person measurement with an optician is recommended.

Our precise measurement method using a reference card achieves accuracy within 1mm, comparable to professional optometry equipment. Unlike other online tools, we account for parallax and eye convergence for true precision. The free iris-based method is less accurate (±2-3mm). See our full accuracy comparison →

The free method uses your webcam to detect your iris and estimate PD. It's quick but less accurate. The premium method uses a standard-sized reference card (credit card, ID card) placed on your forehead for precise calibration, achieving professional-level accuracy.

For the free method, you just need a webcam or phone camera. For the premium method, you'll also need a standard-sized card (credit card, ID card, or library card) to use as a reference.

For visitors in the United States, premium access costs US$2.49 for 24 hours. This gives you unlimited access to all premium tools, including precise pupillary distance and OC height measurement. The price and currency may vary depending on your country.

The premium features require significant development and maintenance to ensure professional-level accuracy. The one-time payment model ensures we can continue improving our tools without relying on ads or selling your data.

No. Since premium access is unlocked immediately upon purchase, no refunds can be provided. By completing your purchase, you expressly consent to immediate access and waive your right of withdrawal. Please try the free method first to ensure your device is compatible before purchasing.

No. All image processing happens entirely in your browser using local JavaScript. Your photos never leave your device and are never uploaded to any server. This is a core privacy guarantee of PupiMetric.

We only collect the minimum data necessary: your email address for account management and payment information processed securely by Stripe. We do not collect or store any photos or measurement data on our servers.

You can delete your account at any time from the Account Settings page. This will permanently remove all your data from our systems.