Safety & PPE Reference Library · Sizing, Fit & Identification

Prescription Eyewear Measuring (PD and Frame Size)

How pupillary distance and the eye size, bridge and temple numbers on a frame are measured and read, and what Z87.1 marks a prescription safety frame and lens must carry.

Ref SP-0316ANSI/ISEA Z87.1

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Prescription (Rx) safety eyewear has to fit the face and line up the optical center of each lens with the pupil. Two sets of measurements matter. Pupillary distance (PD) is the distance between the centers of the pupils. Frame size is printed on the frame as three numbers: eye size, bridge and temple length. ANSI/ISEA Z87.1 adds marking rules for Rx safety frames and lenses.

How to read it

Look inside a temple arm or on the bridge for a marking such as 52□18 140.
The first number is the eye size: lens width in millimeters.
The box symbol separates eye size from bridge. The second number is the bridge: the gap between lenses in millimeters.
The last number is the temple length in millimeters.
Z87.1 Rx frames carry Z87-2. Rx safety lenses carry the lab or maker's mark, and a + if they meet high impact.

Measurements

Measurement	Unit	How it is taken	Why it matters
Distance PD	mm	Pupil center to pupil center, looking at a distant point	Centers the lenses for distance vision
Near PD	mm	Same, looking at a near point; smaller than distance PD	Reading and close work lenses
Monocular PD	mm	Each pupil to the center of the nose bridge	More accurate for faces that are not symmetric
Eye size	mm	Horizontal width of the lens opening	Overall frame width and lens blank size
Bridge	mm	Gap between lenses at the nose	Comfort and how high the frame sits
Temple length	mm	Hinge to the end of the arm, along the arm	Keeps the frame stable behind the ear

Key points

PD and the prescription come from an eye care professional. The distributor's job is to match a compliant frame and route the order to a qualified lab.
Side protection is required where there is a flying-object hazard (29 CFR 1910.133(a)(2)). Use side shields made for the frame, or wraparound frames.
The frame and lenses must both be marked. A Z87-2 frame with street lenses is not a safety device.
Fit check: the frame should sit level, not touch the cheeks, and not slide down when the wearer looks down.
Goggles or face shields worn over Rx glasses (OTG styles) are an alternative for short tasks.

Common mistakes

Reading the bridge number as the PD.
Ordering by frame size alone without a current PD.
Fitting removable side shields from another brand.
Accepting a frame without the Z87-2 mark for Rx safety lenses.

Governing standards: ANSI/ISEA Z87.1; 29 CFR 1910.133.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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