Why isn’t PD printed on my prescription?

A prescription specifies lens power; PD is a dispensing measurement taken when glasses are made. Ask for it at your fitting. We provide it with glasses made in our optical.

How accurate does a home PD need to be?

Within about 1–2 mm for low prescriptions. Above ±4.00 D, in progressives, or with prism, small errors become visible strain — have it measured on instruments.

What’s the difference between PD and OC height?

PD centers the lens horizontally; optical-center and seg height center it vertically for your chosen frame. Progressives need both, which is another reason they’re measured in person.

Are phone PD apps accurate?

Camera apps estimate reasonably at low powers but drift with angle and distance. The card-calibrated ruler plus the marker method is usually as good, and instruments beat both.

Do you measure PD at Cohenmehr?

Yes — a dispensing-grade measurement is part of every glasses fitting in our optical, along with frame-specific centration for progressives and high prescriptions.

Medically reviewed by Dr. Bijan Cohenmehr, OD Last reviewed October 24, 2026

Pupillary distance, explained.

The sixty-odd millimeters that decide whether your lenses center on your eyes.

PD is the distance between your pupils in millimeters. Lenses are ground so their optical centers sit exactly there — miss by a few millimeters and you get strain, pulling and edge distortion, especially in stronger prescriptions.

The home method

Calibrate, then measure.

01PD literacy

Four facts that demystify the number.

PD is simple to understand and fussy to measure well, which is why it’s measured, not guessed, whenever the prescription is strong or the lens is progressive.

01
Typical ranges: Adults usually measure 54–74 mm; children 43–58 mm. Most adults land near 61–64.
02
Single vs dual: Dual PD (e.g. 31.5/30.5) measures each eye from the nose bridge, because faces aren’t symmetric and strong lenses care.
03
Distance vs near: Your eyes converge to read: near PD runs about 3 mm tighter than distance PD. Reading-only glasses use the near number.
04
Why offices measure it: High prescriptions, progressives and prism tolerate roughly a millimeter of error. Dispensing instruments measure to that precision; rulers approximate it.

Common questions

PD, answered.

Anything else, call the office at 310-828-2010.

A prescription specifies lens power; PD is a dispensing measurement taken when glasses are made. Ask for it at your fitting. We provide it with glasses made in our optical.
Within about 1–2 mm for low prescriptions. Above ±4.00 D, in progressives, or with prism, small errors become visible strain — have it measured on instruments.
PD centers the lens horizontally; optical-center and seg height center it vertically for your chosen frame. Progressives need both, which is another reason they’re measured in person.
Camera apps estimate reasonably at low powers but drift with angle and distance. The card-calibrated ruler plus the marker method is usually as good, and instruments beat both.
Yes — a dispensing-grade measurement is part of every glasses fitting in our optical, along with frame-specific centration for progressives and high prescriptions.

Go deeper

Measured right, made right.

A PD is one of a dozen measurements that make a pair of glasses feel effortless. The optical at our eye clinic in Los Angeles takes all of them and then builds the lenses to your frame, your face and your prescription.

Visit the Optical Or call 310-828-2010