What Is Pupillary Distance (PD) and How Do You Measure It?

Pupillary distance, or PD, is the distance between the centers of your pupils. It is measured in millimeters and used when positioning prescription lenses in a frame.

A glasses prescription tells the lab what optical power each lens needs. PD helps indicate where that correction should sit in relation to your eyes. That is why an online glasses order may ask for PD even when it is not printed beside SPH, CYL, or AXIS.

Single PD and dual PD

PD can be recorded in two common formats.

Single PD

A single PD is one measurement from the center of one pupil to the center of the other. It might appear as a number such as 62 mm or 64 mm.

Dual PD

Dual PD uses two measurements: from the center of the bridge of the nose to each pupil. It may appear as 31/32 mm or as separate right and left values.

Do not divide a single PD automatically unless the ordering instructions specifically allow it. Faces are not always perfectly symmetrical, so two monocular measurements may not be identical.

Where can you find your PD?

Your PD may be:

• printed on your eyeglass prescription;
• recorded separately by the optical practice;
• available in your patient records; or
• measured by an optician or another qualified eye care professional.

If the number is not shown, ask the provider who measured you whether it is available. A professional measurement is the best starting point, particularly for progressive lenses or prescriptions that require more precise fitting.

Can PD be measured at home?

An at-home measurement can be a practical reference, but small errors are easy to make. Use a ruler marked in millimeters, repeat the measurement, and do not submit a result that changes significantly from one attempt to the next.

A careful two-person method

1. Sit upright in even lighting with your face directly in front of the person helping you.
2. Hold a millimeter ruler level just below your eyes, or ask your helper to hold it without pressing against your face.
3. Keep your head still and look at your helper’s left eye.
4. Have your helper align the zero mark with the outer edge of your right pupil.
5. Without moving the ruler, look at your helper’s right eye.
6. Have your helper read the mark aligned with the inner edge of your left pupil.
7. Repeat the measurement at least three times and use the result only if the readings are consistent.

Keep the ruler level throughout the process and record the result in millimeters, not inches.

If you measure alone

1. Stand in front of a mirror in even lighting, about 18 inches away.
2. Hold a millimeter ruler level just below your eyes.
3. Close your left eye and use your right eye to align the zero mark with the center of your right pupil.
4. Keep the ruler still, open your left eye, and close your right eye.
5. Read the millimeter mark aligned with the center of your left pupil.
6. Repeat the process several times.

Mirror measurements can be affected by head movement, viewing angle, and parallax. If repeated results do not agree, stop and seek a professional measurement instead of averaging uncertain numbers.

Distance PD and near PD

You may see references to distance PD and near PD. The eyes naturally turn inward when focusing at a close distance, so these measurements are not always the same.

Use the PD requested for the type of glasses you are ordering. Do not subtract a fixed number or convert one measurement into another without guidance from an eye care professional.

Why progressive lenses deserve extra care

Progressive lenses blend distance, intermediate, and near zones within one lens. Their performance depends not only on the written prescription but also on accurate lens positioning and frame fit.

For that reason, a professional PD measurement is strongly preferable for progressive orders. The prescription must also include an ADD value.

Common PD mistakes to avoid

• measuring in inches and converting approximately;
• holding the ruler at an angle;
• moving your head or the ruler during the measurement;
• confusing a single PD with one side of a dual PD;
• copying another person’s measurement;
• guessing when repeated results are inconsistent; or
• using a near PD when the order requests distance PD.

Before you enter PD online

Check whether the configurator requests one number or separate right and left values. Enter the measurement in the same format in which it was provided. If the format is unclear, contact us before completing the order.

Read the Prescription Guide

Frequently asked questions

Is PD part of my prescription?

PD is an important measurement used to make prescription lenses, but it may be recorded separately from the refractive prescription. Ask your eye care provider if you do not see it.

Does PD change?

Adult PD is generally stable, but the measurement used for a particular order can depend on whether the glasses are intended for distance or near use. Confirm rather than assume.

Can I use the PD from an old pair of glasses?

Use a documented measurement from a reliable source when possible. If you are uncertain how the old value was obtained or which PD format it represents, have it checked.

What should I do if three measurements are different?

Do not guess or average widely different results. Ask an optician or eye care professional to measure your PD.

This article is general educational information and is not a substitute for an eye examination or professional fitting advice.