What is interpupillary distance?

The straight-line distance between the centre of your left pupil and the centre of your right pupil, expressed in millimetres. It is a standard measurement used when fitting prescription lenses and is a stable anchor point in facial proportion work.

How Facemap measures interpupillary distance

This is the one measurement on Facemap reported in real-world millimetres rather than as a ratio, and the method is worth explaining plainly. MediaPipe Face Mesh includes dedicated iris landmarks, and the human iris has a famously consistent horizontal diameter of approximately 11.7 millimetres across adults, varying only slightly by individual. The scan measures your iris diameter in pixels, uses the 11.7 millimetre constant to derive a pixel-to-millimetre conversion factor for that exact frame, then applies the same factor to the pixel distance between your two pupil centres. Because the calibration is recomputed from your own iris in every frame, it self-corrects for how close you are sitting to the camera and for differences between devices.

What the typical range looks like

Adult interpupillary distance typically falls between 54 and 68 millimetres, with the average sitting close to 63 millimetres. There is no better or worse value, it is simply a fixed structural measurement used mainly for practical fitting purposes.

How to read your result

IPD is most useful as a stable reference distance rather than an aesthetic score. Once you have it in real millimetres, other Facemap measurements that are normally reported only as ratios, such as eye spacing, can in principle be cross-checked against a known physical scale.

The interpupillary distance formula: how we calculate it

Pupil separation as a fraction of your own bizygomatic width. Landmark numbers are MediaPipe Face Landmarker indices, and every distance is normalised to your own face so camera distance and image size cancel out.

dist(468, 473) / dist(234, 454)

Landmarks used

468, 473 (iris centres), 234, 454

Reference target

0.46

Tolerance band

0.08

Your reading is compared with that published reference on a Gaussian match curve: score = round( 100 x exp( -0.5 x ( (reading - target) / tolerance )^2 ) ), clamped to 1 to 99. Basis for the reference value: adult interpupillary to face width ratios in anthropometric data. The headline Attractiveness Score works differently: all readings are corrected for head angle and expression, weighted by confidence and mapped onto a 1 to 100 scale by a model calibrated against a published research set of more than Facemap scans.

Read the full Facemap methodology, including how the 22 measurement categories combine into your Attractiveness Score.

Interpupillary distance reference table

Interpupillary distance bands in adults.

• Below 54 mmNarrow

  Below the typical adult range

• 54 to 60 mmBelow average

  Common in smaller facial frames

• 61 to 68 mmAverage to wide

  The most commonly measured adult band

• Above 68 mmWide

  Above the typical adult range

Why the iris is used to calibrate millimetre measurements

Camera images give you pixels, not millimetres, and pixel distances change with how close a face sits to the lens. The iris solves this because its horizontal diameter is remarkably consistent across adults, at roughly 11.7 millimetres, regardless of eye colour or overall face size. By measuring how many pixels your iris spans in a given frame, the scan derives an exact millimetre-per-pixel value for that frame and applies it to any other distance measured in the same image, including your pupil to pupil distance.

Interpupillary distance and glasses fitting

Opticians use PD to centre lenses correctly over your pupils, since a lens optical centre placed away from the pupil introduces unwanted prismatic effect. Facemap's reading gives you a reference figure, but a dispensing optician's in-person measurement remains the appropriate source for an actual lens order.

Monocular PD and why Facemap reports a single figure

Some optical prescriptions ask for a monocular PD, the distance from each pupil to the centre of the nose bridge, measured separately per eye. Facemap currently reports total interpupillary distance as a single combined figure between the two pupil centres, which is the more commonly requested value for general facial measurement purposes.

The interpupillary distance formula, step by step

The IPD calculator converts a pixel measurement into millimetres using a single reliable constant: the known 11.7 millimetre average diameter of the human iris.

• /Measure the horizontal diameter of one iris in pixels for the current frame
• /Divide the known 11.7mm iris diameter by that pixel measurement to get a millimetres-per-pixel factor
• /Measure the pixel distance between the centres of your two pupils
• /Multiply that pupil to pupil pixel distance by the millimetres-per-pixel factor
• /The result is your interpupillary distance in real millimetres