An IP rating is a two digit code defined by IEC 60529 that states exactly how well an enclosure resists solid objects and dust, then separately, liquids, nothing more and nothing less.
This guide breaks down what each digit actually tests, why IP66 and NEMA 4X are not the same thing despite looking similar, and includes a selector that recommends a minimum IP rating for common field environments.
IP rating stands for Ingress Protection rating, a two digit code defined by IEC 60529.
The first digit rates protection against solid objects and dust on a scale of 0 to 6, and the second digit rates protection against liquids on a scale of 0 to 9, with a separate 9K tier for hot high pressure jets.
Each digit is tested and certified independently, which is exactly why a rating like IP66 tells an engineer something precise: dust tight, plus protected against powerful water jets from any direction, nothing vaguer than that.
Datasheets throw IP ratings around constantly, IP65 enclosure, IP67 sensor, IP68 connector, without most readers knowing what a single digit actually changed between them.
The code is not a vague marketing scale. Each digit corresponds to a specific, repeatable laboratory test defined in IEC 60529, and the two digits are completely independent of each other.
This article works through both digits in full, how IP compares to the separate NEMA and IK standards, and a selector tool that recommends a minimum rating for common installation environments.
What an IP Rating Code Actually Encodes
The letters IP stand for Ingress Protection, defined by the international standard IEC 60529. The code always follows the same format: the letters IP, followed by exactly two digits.
The first digit measures protection against solid foreign objects, including dust, on a scale from 0, no protection, to 6, completely dust tight.
The second digit measures protection against liquids, from 0, no protection, to 9, with a separate 9K classification for road vehicle washdown conditions.
An X can replace either digit when that specific protection was not tested or is not being claimed, for example IPX7 states liquid protection only, with no claim made about solid particle protection at all.
First Digit: Solid Particle and Dust Protection
Each level in the first digit corresponds to a minimum object size the enclosure is verified to keep out, using an actual test probe of that size.
| Digit | Protection Level | Test Detail |
|---|---|---|
| 0 | None | No protection against solid objects |
| 1 | Large objects | Blocks objects larger than 50 mm, such as the back of a hand |
| 2 | Medium objects | Blocks objects larger than 12.5 mm, such as a finger |
| 3 | Small objects | Blocks objects larger than 2.5 mm, such as a tool |
| 4 | Wire sized objects | Blocks objects larger than 1 mm, such as a wire |
| 5 | Dust protected | Limited dust ingress permitted, but not enough to cause harm |
| 6 | Dust tight | No dust ingress at all under test conditions |
Second Digit: Liquid and Water Protection
The second digit scale runs from no protection to continuous submersion, and the jump between adjacent numbers is not evenly spaced, the test conditions change significantly at several points on the scale.
| Digit | Protection Level | Test Detail |
|---|---|---|
| 0 | None | No protection against liquids |
| 1 | Vertical drips | Protected against vertically falling drops |
| 2 | Tilted drips | Protected against drips when tilted up to 15 degrees |
| 3 | Spray | Protected against spray up to 60 degrees from vertical |
| 4 | Splashing | Protected against splashing from any direction |
| 5 | Low pressure jets | Protected against a 6.3 mm nozzle jet at 12.5 liters per minute |
| 6 | High pressure jets | Protected against a 12.5 mm nozzle jet at 100 liters per minute |
| 7 | Temporary immersion | Protected to 1 meter depth for 30 minutes |
| 8 | Continuous immersion | Protected beyond 1 meter, exact depth defined by the manufacturer |
| 9K | Hot high pressure jets | Protected against close range hot, high pressure washdown, common in vehicle and hygienic applications |
IP65, Dust Tight, Low Pressure Jets
A common baseline for outdoor field enclosures and general purpose sensors exposed to weather.
IP66, Dust Tight, High Pressure Jets
The step up for washdown environments, food processing lines, and heavier weather exposure.
IP67, Temporary Immersion
Survives brief submersion to 1 meter, common for handheld devices and connectors near flood risk.
IP68, Continuous Immersion
Rated for sustained submersion, the depth and duration are set by the specific manufacturer.
Anatomy of an IP Code
IP Rating Selector for Common Environments
Select the environment closest to the actual installation to see a general minimum IP rating guideline. This is a starting point for a conversation with a qualified engineer, not a substitute for a proper site specific hazard assessment.
IP Rating vs NEMA Rating: They Are Not Interchangeable
NEMA ratings, common in North America, and IP ratings both describe enclosure protection, and the two are often mistakenly treated as a simple lookup table between them.
They are not equivalent. IP ratings test only dust and liquid ingress. NEMA types also account for corrosion resistance, ice formation, gasket aging, and in some types, hazardous location containment, none of which the IP scale tests at all.
| Rough Comparison | Key Difference |
|---|---|
| NEMA 4X approximately near IP66 | NEMA 4X adds corrosion resistance and ice resistance that IP66 does not test at all |
| NEMA 12 approximately near IP55 | NEMA 12 emphasizes indoor oil and coolant resistance, not outdoor weather |
| NEMA 3R approximately near IP54 | NEMA 3R specifically targets rain, sleet, and ice, a different test method than IP |
IK Impact Rating: A Different Number Entirely
IK ratings are frequently confused with IP ratings, but they measure something completely different: mechanical impact resistance, not ingress protection.
The IK scale measures impact energy in joules a housing can absorb without damage. IK08 corresponds to about 5 joules, roughly a 1.7 kilogram object dropped from 0.3 meters.
IK10, the highest common tier, corresponds to about 20 joules. Public area and demanding industrial installations commonly specify at least IK08 alongside whatever IP rating the environment requires.
IP Rating Selection Do's and Don'ts
✓ Do
- Read both digits together, a strong second digit does not compensate for a weak first digit or vice versa
- Confirm the exact standard, IP, NEMA, or both, actually required for the project, rather than assuming equivalence
- Check IK impact rating separately when mechanical damage risk exists, it is not part of the IP code
- Verify the manufacturer's stated depth and duration for any IP68 claim, the standard leaves that number to them
✗ Don't
- Assume IP66 and NEMA 4X are interchangeable on a specification sheet, they test different things
- Treat an X in an IP code as zero protection, it means untested or unclaimed, not necessarily unprotected
- Assume a higher second digit always implies a higher first digit, the two scales are independent
- Select an enclosure rating based on marketing language alone without checking the actual tested digits
Resources on IP Ratings and Enclosure Standards
IP Rating Explained, Questions Engineers Ask
External References
- Standard Clarity: IP Ratings Explained, Complete IP Code Chart and Meanings
- Paya Press: IP vs NEMA Ratings and IK, Full Comparison
What We Learn Today
- An IP rating is a two digit code from IEC 60529, first digit for solid particles and dust, second digit for liquids, each tested independently.
- Common field ratings, IP65 through IP68, share the same dust tight first digit, six, and differ only in the water protection level of the second digit.
- IP ratings and NEMA ratings are not interchangeable, NEMA also tests corrosion, ice, and gasket performance that IP does not cover at all.
- IK impact rating is a separate scale entirely, measuring mechanical impact resistance in joules, not ingress protection.