Pupillary Distance Measurement Tool + Printable PD Ruler
Measure pupillary distance (PD) at home with a printable 1:1 ruler, a mirror or a helper, and three repeated readings. This MVP does not request camera access.
Step 1: Choose how you will measure
For distance PD, keep the head level and use a distant fixation target so the eyes are not converging on the ruler.
Measurement method
PD format
Privacy note: this tool does not request camera access or upload the PD values entered below. Calculations run in the browser session.
Step 2: Print and calibrate the PD ruler
The printable ruler is designed for 100% / Actual Size. Do not use “Fit to page.”
85.60 mm card check
A standard ISO/IEC ID-1 payment card is 85.60 mm wide. After printing, place a physical card over the calibration box on the printed sheet. The card width should match the box.
The line above is only an on-screen illustration. Use the printed 85.60 mm box for the actual scale check.Why calibration matters: browser zoom does not determine printed size, but printer scaling does. A ruler printed at 95% or 105% creates the same percentage error in the PD reading.
Step 3: Measure three times
Single / binocular distance PD
Dual / monocular distance PD
Near PD
Use the near-fixation method recommended for the eyewear task or prescription. Enter three separately measured readings.
Step 4: Your PD result
Your three-reading median:
This result supports at-home eyewear measurement only. It is not an eye exam, diagnosis, or substitute for professional spectacle fitting.
Use professional measurement for progressive/multifocal lenses, prism prescriptions, strong prescriptions, unusual facial asymmetry, or results that remain inconsistent after repeating the process. Progressive fitting can require more than PD alone, including fitting height and frame-position measurements.
What is pupillary distance (PD)?
Pupillary distance is the distance, measured in millimeters, between the centers of the pupils or from the facial midline to each pupil. Eyewear labs use PD to position the optical center of lenses relative to the wearer’s eyes.
PD is a fitting measurement rather than a measure of refractive power. SPH, CYL and AXIS describe lens power; PD describes where that lens power should sit horizontally in front of the eyes.
Single PD vs dual PD vs near PD
| PD type | What it records | Typical use |
|---|---|---|
| Single / binocular PD | One number spanning pupil center to pupil center. | Common distance-PD format for many single-vision orders. |
| Dual / monocular PD | Separate OD and OS distances from the facial midline. | Useful when the face or pupil position is asymmetric and commonly used in more precise spectacle fitting. |
| Near PD | PD while the eyes are converged on a near fixation target. | Near-vision tasks and some multifocal or occupational fitting workflows. |
Do not create dual PD by simply dividing a single PD in half. Real faces are not perfectly symmetrical, so right and left monocular PD values can differ.
How to measure PD at home with a mirror
- Print the ruler at 100% / Actual Size and verify the 85.60 mm calibration box with a physical payment card.
- Stand roughly 20 cm (8 in) from a mirror with the head level.
- For distance PD, look at a distant fixation target rather than focusing on the ruler itself.
- Measure either pupil-center to pupil-center for single PD, or midline-to-pupil separately for dual PD.
- Remove and reposition the ruler, then repeat the measurement two more times.
- Use the median of the three readings. If the set varies by more than 2 mm, repeat the set.
How a friend can measure your PD
- Keep the head straight and look at a distant target beyond the helper.
- The helper holds the ruler level at eye height without blocking your line of sight.
- For single PD, align 0 with one pupil center and read the mark at the other pupil center.
- For dual PD, center the ruler on the facial midline and read OD and OS separately.
- Reset the ruler between measurements and record three independent readings.
Why at-home PD measurements can be wrong
- Print scaling: “Fit to page” changes the physical ruler scale.
- Looking at the ruler: near fixation makes the eyes converge and can reduce a distance-PD reading.
- Head rotation or tilt: changes the apparent pupil position.
- Ruler angle: a ruler that is not horizontal introduces parallax and alignment error.
- One-shot measurement: small placement changes are why this tool asks for three readings and uses the median.
- Assuming perfect symmetry: dividing a single PD by two can hide real OD/OS differences.
When should PD be measured professionally?
Professional fitting is the safer choice when lens performance depends on more than a simple horizontal PD. Progressive or multifocal lenses can require monocular distance PD, fitting height, frame position and other dispensing measurements. Prism prescriptions and high-power prescriptions also make centration errors more consequential.
Professional measurement is also appropriate when repeated home readings remain inconsistent, the eyes or facial features are notably asymmetric, or the eyewear provider specifically requires a fitting measurement taken with the chosen frame.
Privacy and the future camera version
This MVP is intentionally camera-free. The page uses manual ruler measurements and performs calculations in the browser session. No photo, video or entered PD value is uploaded by this code.
A future camera-assisted version should preserve that privacy model by performing face-landmark detection locally on the device wherever technically practical, rather than requiring raw face images to be uploaded to a remote server.
PD measurement FAQ
What does PD mean on a glasses prescription?
PD means pupillary distance. It is a lens-positioning measurement in millimeters, not a refractive-power value such as SPH or CYL.
Is single PD the same as binocular PD?
Yes. A single or binocular PD is one overall pupil-center-to-pupil-center distance.
Is dual PD the same as monocular PD?
Dual PD usually refers to two monocular values: one for the right eye (OD) and one for the left eye (OS), each measured from the facial midline.
Can I divide single PD by two to get dual PD?
That produces two equal mathematical halves, but it does not measure the actual monocular PD of each eye. Facial and pupil-position asymmetry can make OD and OS different.
Why does this tool take three PD readings?
Repeated placement helps expose measurement variation. The tool uses the median of three readings so one unusually high or low reading does not determine the result.
Can I use this for progressive lenses?
Use professional fitting for progressive or multifocal lenses. PD is only one part of the fitting process; fitting height and frame-specific measurements may also be required.