How to Measure Pupillary Distance (PD) at Home

Pupillary distance, usually abbreviated as PD, is the distance measured in millimeters between the centers of your pupils. It is one of the measurements used to position prescription lenses so their optical centers align appropriately with your eyes.

Binocular PD vs. monocular PD

Binocular PD is a single number measuring from the center of one pupil to the center of the other. Monocular PD records the distance from the center of the nose bridge to each pupil separately, often written as right/left values.

Monocular measurements can be useful when the face or pupil positions are not perfectly symmetrical, and some lens designs or ordering systems may require more detailed fitting measurements.

What you need

• A millimeter ruler or a ruler designed for PD measurement.
• A mirror with good lighting, or another person who can help.
• A steady head position and a distant visual target to reduce unnecessary eye movement.

If you want a dedicated reference tool, EBJDE offers Pupillary Distance (PD) Measurement Rulers for eyewear fitting and general measurement reference. For additional measurement and workshop references, browse our optical tools and testing accessories.

How to measure binocular PD in a mirror

1. Stand or sit directly in front of a mirror and keep your head level.
2. Hold the millimeter ruler horizontally across the bridge of your nose, close to the eyes without touching them.
3. Close your right eye and align the 0 mm mark with the center of your left pupil.
4. Without moving the ruler, open your right eye and close your left eye.
5. Read the millimeter mark that crosses the center of your right pupil. That is your approximate binocular PD.
6. Repeat the measurement at least two or three times. If the readings vary, reposition carefully and measure again rather than averaging obviously inconsistent results.

How another person can help

Ask the helper to stand directly in front of you while you look at a distant point behind them rather than following the ruler with your eyes. The helper can align 0 mm with the center of one pupil and read the center of the other. Keeping both your head and the ruler level helps reduce measurement error.

How to measure monocular PD

For monocular PD, measure from the centerline of the nose bridge to the center of each pupil separately. Record the right and left values rather than assuming they are identical. The two monocular values should approximately add up to the binocular PD, but small differences in technique are common with home measurements.

Common measurement mistakes

• Using centimeters instead of millimeters.
• Tilting the ruler or moving your head between readings.
• Looking at the ruler instead of maintaining a consistent viewing direction.
• Measuring from the edge of the pupil instead of its center.
• Relying on a single reading when repeat measurements disagree.

When should PD be measured professionally?

A home PD can be useful as a reference, but it is not a substitute for all professional fitting measurements. Progressive, multifocal, prism and other more complex lens designs may require additional measurements such as fitting height, frame dimensions or monocular centration. Stronger prescriptions can also be more sensitive to centration errors.

If accurate lens positioning is critical for the eyewear you are ordering, confirm the required measurements with a qualified optician or eye-care professional. PD is only one part of prescription lens planning; for how refractive index, frame size and lens thickness work together, see How to Choose a Lens Index.

Keep the measurement with your eyewear records

Once you have a reliable PD, record whether it is binocular or monocular and note the units in millimeters. Keeping the measurement alongside your prescription and frame information makes it easier to compare future eyewear orders without confusing different measurement formats.