ANSI Z87.1 vs EN 166: reading the other stamp on your safety glasses

Two standards, two marking systems

If you have bought safety or shooting glasses in the last few years, you have probably seen a frame stamped with something like Z87+ on one temple and EN 166 FT or CE 1 F on the other, and wondered which one counts. Both count, for different purposes. ANSI/ISEA Z87.1 is the American national standard for eye and face protection. EN 166 is the European standard, and it is the one behind the CE mark on eyewear sold in the EU and the UKCA mark in Britain.

Makers who sell into both markets test to both and stamp both, which is why dual marks are so common on the better frames. That is good news — it means more independent testing, not less — but the two systems encode their results completely differently, and a letter that means one thing in one system can mean something else entirely in the other. The clearest example: in EN 166, S is an impact class. Under Z87.1, S on a lens means a special-purpose filter. Same letter, unrelated meanings.

This page is the translation key. It assumes you have already read what Z87 means — if not, start there, because the American marks are the ones that govern anything you buy and wear in the United States.

What ANSI Z87.1 tests

Two impact tests decide whether a pair earns the plus, and both are physical tests on a complete lens-and-frame assembly rather than on a lens alone.

The high-mass test drops a 500 g pointed weight from 50 inches onto the lens. The high-velocity test fires a quarter-inch steel ball at 150 feet per second — about 102 miles per hour, or roughly 46 m/s. Pass both and the maker may mark the product Z87+. Pass only the basic drop-ball requirement and the mark is a plain Z87.

That is the whole hierarchy. Z87.1 adds plenty of other letters for other hazards — U for UV filtering, L for visible light, W for welding, D3 for splash, D4 for dust — but on impact there are two levels, and the plus is the one that matters on a firing line or at a grinder. The marks are laid out in full on Z87 vs Z87+, and the current edition's changes to anti-fog criteria and marking are covered in what Z87 means.

What EN 166 tests, letter by letter

EN 166 does not use a plus. It uses a letter for mechanical strength, and the letter tells you the speed of the projectile the eyewear survived. A 6 mm steel ball is fired at the lens, and the class depends on how fast.

S — increased robustness. The lowest mechanical-strength class, and the one with the least consistent published description across the sources we read. Treat it as a basic strength requirement rather than an impact rating.

F — low-energy impact, particles at up to about 45 m/s. The everyday class: general manufacturing, maintenance, most safety spectacles.

B — medium-energy impact, up to about 120 m/s. Grinding and engineering work. You will usually see B on goggles rather than spectacles, because the frame has to hold the lens through a much harder hit.

A — high-energy impact, up to about 190 m/s. Face shields and the heaviest industrial work.

There is one more letter worth knowing, because it turns up on the best-documented eyewear on this site: T. Appended to the impact letter — FT, BT, AT — it means the impact test was also passed at temperature extremes. An FT mark is therefore better than a plain F: same speed, harder conditions. Revision publishes exactly that for the StingerHawk, citing "EN 166 clause 7.3.4 Protection against high speed particles (FT)", which is the most precise EN citation we have found on any product page — see the Revision StingerHawk review.

Optical class 1, 2 and 3

This is the part of EN 166 that has no direct equivalent in the American mark, and it is genuinely useful information that Z87.1 does not give you on the frame. Optical class describes the visual quality of the lens, and it is stated as a digit: 1, 2 or 3.

Class 1 is for continuous wear — all day, every day, through a full shift. Class 2 is for intermittent use. Class 3 should not be worn for long periods at all, and is typical of face shields and heavy visors where the priority is coverage rather than clarity.

For anything you intend to shoot in, you want class 1 and nothing less. A class 2 or 3 lens is not dangerous, but it has more permitted distortion, and distortion in a lens you are aiming through is a problem you will feel long before you can name it. If a listing shows an EN 166 mark on a pair you plan to wear for hours, the digit beside the letters is the number to look for — and it is a better clarity signal than anything on the American side of the frame, where optical requirements are met but not graded on the stamp.

The field-of-use digits

EN 166 also carries digits for the hazard the eyewear is built for, and they appear before the mechanical strength letter. The ones you will actually meet:

3 for liquids — droplets and splashes. 4 for large dust particles. 5 for gas and fine dust. 8 for electrical work, meaning a short-circuit electric arc. 9 for molten metal and hot solids.

If those sound familiar, it is because Z87.1 encodes the same hazards with its own letters: D3 for splash, D4 for dust and D5 for fine dust. The hazards are universal; only the notation changes. The splash-and-dust end of the American system is covered on safety goggles vs glasses, which is the practical version of the same decision.

Which one is stricter

Here is the honest answer, and it needs the numbers rather than a verdict.

The ANSI Z87.1 high-velocity test uses a quarter-inch (6.35 mm) steel ball at 150 ft/s. EN 166 uses a 6 mm steel ball, and the F class corresponds to about 45 m/s. Convert and those two are remarkably close: 150 ft/s is about 46 m/s, and the projectiles are within a third of a millimeter of each other. So EN 166 F and ANSI Z87+ high-velocity are testing at approximately the same energy. Neither is meaningfully tougher than the other at that level.

Above that, EN 166 keeps going where Z87.1 stops. B is about 120 m/s — roughly 394 ft/s — and A is about 190 m/s, or about 623 ft/s. There is no ANSI impact class above the plus, so a lens marked B or A has survived a demonstrably harder hit than Z87+ requires. That is the one respect in which the European system is more demanding: it has more headroom at the top.

Below that, Z87.1 has something EN 166 does not: the high-mass drop test, a 500 g pointed weight from 50 inches. That is a different failure mode — a heavy slow object rather than a light fast one — and the European impact classes do not cover it the same way. So the two standards are not nested; they test overlapping but different things.

The one place an EN mark is not enough

This is the practical point that justifies the whole page, and it has a clear answer rather than a judgment call.

OSHA's eye and face protection rule, 29 CFR 1910.133, requires that protective devices "comply with any of the following consensus standards" and then names ANSI/ISEA Z87.1-2010, ANSI Z87.1-2003 and ANSI Z87.1-1989 (R-1998) — or be demonstrated to be "at least as effective". EN 166 is not on that list. So a pair of glasses marked only EN 166 1 F, with no Z87 marking anywhere, does not satisfy the rule on its face in a US workplace. An employer can in principle demonstrate equivalence, but that burden falls on the employer, and no safety manager wants to argue it during an inspection.

For your own garage or your own range trip, nobody is inspecting anything and an EN 166 F lens is a real tested lens. But if the glasses are going into a workplace, on a contractor's site, or anywhere a safety officer looks at frames, buy a pair that carries the Z87 mark. The regulation and what it actually requires of you is on OSHA approved safety glasses.

The reverse case is worth a line too. A Z87+-only pair taken to a European worksite has the same problem in mirror image: the EU expects CE and EN 166. If you work across both, the dual-marked frames below are the ones that travel.

Pairs that carry both

Dual marking is the simplest way out of this entire question: if a maker states both standards, you do not have to decide which system to trust. These four do, and they are spread across the price range and the product types deliberately — a ballistic spectacle, a sealed glasses-goggle hybrid, a military goggle and a budget shop pair.

How to read your own glasses

Take the pair you already own and look at the inside of the left temple, then the lens itself near the nose. You are looking for three groups of characters.

On the frame: the maker's mark, then the standard, then the markings. European marking order runs maker, EN 166, field of use, then mechanical strength — so EN 166 3 4 FT is a frame tested for liquid splash and large dust particles at low-energy impact with temperature extremes. On the American side you are looking for Z87 or Z87+ on the frame, and the edition is usually not printed, which is why the maker's page matters.

On the lens: the maker's mark plus the plus sign if it is high impact, and on a European-marked lens the optical class digit first. A lens stamped 1 F is class 1 optics at low-energy impact.

What should worry you: no marks at all. Unmarked eyewear has no claim behind it in either system, which is a different and much worse situation than a lens marked to a standard you were not expecting. The step-by-step version of this inspection is on how to tell if glasses are ballistic rated, and if your marks have worn off the frame entirely, that is one of the retirement triggers on when to replace shooting glasses.

One closing caution on the sources behind this page. EN 166 is a paid standard and we have not bought a copy; the figures above come from manufacturer and safety-supplier technical notes, which agree with each other on optical class and on the F, B and A speeds but describe the S class inconsistently. We have said so above rather than picking the version we liked. Where a number is approximate we have written "about", and the exact conversions between feet per second and meters per second are ours. Our broader method is on how we rate.