Open a red dot sight’s spec sheet and you will hit a code like IPX7, IPX8, IP67 or IP68. It is one of the most misread numbers in optics, partly because two of those digits are doing completely different jobs and one of them is often hidden behind an X. Here is what the code actually certifies, straight from the IEC 60529 standard that defines it.
What the IP code is
IP stands for Ingress Protection. The rating comes from international standard IEC 60529, which sets fixed tests an enclosure has to pass before a manufacturer can print a given number.
A full IP code is the letters “IP” followed by two characters:
- First digit (solids and dust): a number from 0 to 6. It rates how well the housing keeps out solid objects and dust. 6 is the top mark and means dust-tight, with no dust ingress at all.
- Second digit (water): a number from 0 to 8, with an extra 9K level for high-pressure, high-temperature spray. It rates protection against water.
So in IP67, the 6 is the dust score and the 7 is the water score.
The X is the part people miss
When a digit is shown as X, that property was not rated or not tested. It does not mean zero protection. It means the manufacturer has not published a verified figure for that category.
That is why so many optics are listed as IPX7 or IPX8 rather than IP67 or IP68. The maker ran the water-immersion test and is willing to certify it, but did not publish a separate dust-tightness figure. IPX7 reads as “water-rated, dust unspecified.”
The water digits that matter for optics
A red dot sight lives or dies on the second digit, so it pays to know exactly what each level certifies under IEC 60529:
- 6: protection against powerful water jets. Useful context, but a jet test is not an immersion test.
- 7: protection against temporary immersion. The fixed test is submersion in 1 meter of water for 30 minutes.
- 8: protection against continuous immersion beyond 1 meter, under conditions specified by the manufacturer.
That last point is the one to internalize. Level 8 does not have a single fixed depth in the standard. When you see “IPX8 to 20 m for 1 hour,” the 20 meters and the hour are numbers the manufacturer chose and tested, not values written into IEC 60529. Two IPX8 optics can be sealed to very different depths and both be honest.
One more nuance: a higher water digit does not automatically include the jet test. An optic can pass immersion (7 or 8) without being certified against powerful jets (6), because those are separate procedures.
Decoding the common optic ratings
| Rating | First digit (dust) | Second digit (water) | What it certifies |
|---|---|---|---|
| IPX7 | Not rated (X) | 7 | Temporary immersion: 1 m for 30 minutes. Dust not specified. |
| IPX8 | Not rated (X) | 8 | Continuous immersion deeper than 1 m, to the depth and time the maker states. Dust not specified. |
| IP67 | 6 (dust-tight) | 7 | Dust-tight AND temporary immersion to 1 m for 30 minutes. |
| IP68 | 6 (dust-tight) | 8 | Dust-tight AND continuous immersion to the maker’s stated depth and time. |
Many optics list IPX7 or IPX8 specifically because only the water side was tested and published. The missing first digit is a documentation gap, not a sign the housing is open to dust.
What this means for you
Translating the codes into plain shopping advice:
- IPX7: survives a dunk. Rain, sweat, a dropped optic in a puddle, or a creek crossing are all well within range. This covers the vast majority of real-world use.
- IPX8: rated deeper and longer than IPX7, but only to the figure the manufacturer publishes. Always read the actual depth. “IPX8” with no stated depth tells you less than it looks like it does.
- IP6X (the 6 in IP67 or IP68): adds verified dust-tightness on top of the water rating. Worth having if you shoot in dusty, sandy or high-grit environments.
Tie that to real glass. Trijicon rates the RMR Type 2 waterproof to 20 meters (66 feet), an IPX8-class continuous-immersion figure the company set and tested itself, which is far beyond anything a pistol optic meets in normal use. If your concern is weather and debris rather than depth, an enclosed-emitter optic matters as much as the IP number, because a sealed emitter window keeps rain, mud and lint from ever reaching the LED and blocking the dot. The IP code tells you how the housing handles water and dust. The emitter design tells you whether the dot stays visible while it does.
Bottom line: read the second digit first, treat any IPX8 depth as a manufacturer spec rather than a universal guarantee, and remember that an X just means that property was left off the sheet.