Every pair of ear plugs, earmuffs, or hearing protection device sold in the United States has a number on the package: the NRR. You have probably seen it. NRR 22. NRR 27. NRR 33. But what does that number actually tell you? Let’s get into NRR Ratings Explained.

How much protection am I actually getting? The short answer: less than you think. The NRR is not a straightforward “this blocks X decibels of noise” number, and misunderstanding it is one of the most common mistakes workers make when choosing hearing protection.

This guide breaks down what the NRR means, how to use it to estimate your real-world noise exposure, how it compares to the SNR system used outside the United States, and how to pick the right rating for your job.

What Does NRR Stand For?

NRR stands for Noise Reduction Rating. It is a single number, measured in decibels (dB), that indicates how much a hearing protection device reduces noise under ideal laboratory conditions.

The key phrase there is “ideal laboratory conditions.” The NRR is determined through standardized testing (ANSI S3.19 or the newer ANSI S12.6) where the device is fitted perfectly on test subjects in a controlled acoustic environment. On a real job site, with sweat, movement, imperfect fit, and hair in the way, the actual noise reduction is lower.

That gap between the lab rating and real-world performance is something every worker should understand.

How to Calculate Real-World Noise Reduction

OSHA and NIOSH use different methods to estimate how much protection you actually get from a given NRR. Here is the most common calculation, which OSHA uses:

Step 1: Take the NRR number on the packaging.

Step 2: Subtract 7.

Step 3: Divide the result by 2.

That gives you the estimated real-world noise reduction in decibels.

Example with NRR 27 ear plugs (like PermaPlug):

(27 – 7) / 2 = 10 dB of estimated real-world reduction

So if you are working in a 95 dB environment with NRR 27 ear plugs, your estimated exposure drops to about 85 dB, which is right at the OSHA action level.

This might seem like a big gap from the advertised 27 dB, but it reflects the reality that most people do not achieve a perfect seal every time they insert ear plugs. Proper fit technique makes a significant difference, which is why learning to insert your ear plugs correctly matters almost as much as choosing the right NRR.

NIOSH uses an even more conservative estimate for ear plugs specifically: they recommend derating the NRR by 50% (multiply by 0.5) instead of using the OSHA formula. Under the NIOSH method, NRR 27 ear plugs would give you an estimated 13.5 dB of real-world reduction. The NIOSH approach builds in a larger safety margin, which is especially relevant for workers who are exposed to noise for full 8-hour shifts.

How Loud Is Your Job? Common Noise Levels

To know if your hearing protection is adequate, you need to know how loud your work environment is. Here are typical decibel levels for common tools and situations:

Under 85 dB (generally safe without protection):

  • Normal conversation: 60-70 dB
  • Vacuum cleaner: 70-75 dB
  • City traffic from inside a car: 80-85 dB

85-100 dB (hearing protection recommended or required):

  • Hand drill: 85-90 dB
  • Lawn mower: 85-90 dB
  • Shop vacuum: 85-90 dB
  • Belt sander: 90-95 dB
  • Circular saw: 90-100 dB
  • Tractor: 90-95 dB

100-115 dB (hearing protection required):

  • Table saw: 100-105 dB
  • Chainsaw: 105-115 dB
  • Jackhammer: 100-110 dB
  • Impact wrench: 100-110 dB
  • Nail gun: 100-110 dB
  • Angle grinder: 100-110 dB

Over 115 dB (hearing protection critical):

  • Hammer drill on concrete: 110-120 dB
  • Ambulance siren at close range: 120 dB
  • Gunshot: 140-170 dB

OSHA requires employers to provide hearing protection and implement a hearing conservation program when worker noise exposure reaches 85 dB averaged over an 8-hour shift. At 90 dB, engineering or administrative controls are required in addition to hearing protection.

What NRR Do You Need?

Your goal is to get your effective noise exposure below 85 dB. Here is how different NRR ratings perform across common noise levels, using the OSHA derating formula:

NRR 22 (estimated real-world reduction: 7.5 dB)

  • 90 dB environment → ~82.5 dB (adequate)
  • 100 dB environment → ~92.5 dB (not adequate)
  • Best for: light-duty tasks, lawn mowing, shop work under 95 dB

NRR 27 (estimated real-world reduction: 10 dB)

  • 95 dB environment → ~85 dB (adequate)
  • 100 dB environment → ~90 dB (marginal; okay for shorter exposure)
  • 110 dB environment → ~100 dB (not adequate alone)
  • Best for: general construction, power tools, manufacturing, most job sites

NRR 33 (estimated real-world reduction: 13 dB)

  • 100 dB environment → ~87 dB (adequate)
  • 110 dB environment → ~97 dB (marginal)
  • Best for: heavy equipment, chainsaws, extended high-noise exposure

For extremely loud environments over 105 dB, consider doubling up: wearing ear plugs under earmuffs. When you combine two devices, you do not add their NRR numbers together. Instead, take the higher NRR and add 5 dB. So NRR 27 plugs under NRR 25 earmuffs gives you an effective NRR of about 32, which translates to roughly 12.5 dB of estimated real-world reduction using the OSHA formula.

NRR vs. SNR: What Is the Difference?

If you buy hearing protection made in Europe or see products with international certifications, you may notice an SNR rating instead of (or alongside) the NRR. They measure the same thing, noise reduction capability, but they use different testing standards and different math.

NRR (Noise Reduction Rating): Used in the United States. Tested per ANSI S3.19 or ANSI S12.6. Measured in C-weighted decibels and subtracted from C-weighted noise measurements (or derated and subtracted from A-weighted measurements using the formulas above).

SNR (Single Number Rating): Used in Europe and internationally. Tested per EN 352/ISO 4869-2. Generally produces a higher number than NRR for the same device because of differences in the testing method and calculation.

A product rated NRR 27 might carry an SNR of 34. Those are not contradictory; they just reflect different measurement standards. You cannot directly compare NRR and SNR numbers or use the OSHA derating formula on an SNR value.

When in doubt, use the NRR number for any calculations related to OSHA compliance in the United States.

Why a Higher NRR Is Not Always Better

It might seem logical to always grab the highest NRR available, but overprotection can create its own problems:

  • Communication: If you cannot hear coworkers, warning signals, or equipment alarms, that is a safety hazard. Workers who feel isolated by their hearing protection are more likely to remove it or wear it improperly.
  • Comfort: Higher NRR devices often achieve their rating through a tighter seal or denser material, which can mean more ear canal pressure and discomfort over long shifts.
  • Compliance: The most protective ear plug in the world does nothing if your crew takes them out after 20 minutes because they are uncomfortable. The best hearing protection is the one people actually wear.

The ideal NRR brings your exposure below 85 dB without cutting you off from your environment. For most construction and manufacturing settings, NRR 25-30 hits that sweet spot.

What About Fit?

The NRR assumes proper insertion. With ear plugs, “proper insertion” means the plug is deep enough in the ear canal to create a complete seal. Most people do not insert ear plugs deeply enough, which is the single biggest reason real-world protection falls short of the lab rating.

Signs your ear plugs are not inserted correctly:

  • You can still hear conversations clearly at normal volume
  • The plug feels like it is sitting in the opening of your ear rather than inside the canal
  • The plug slides out or loosens on its own during work

Triple-flange designs (like PermaPlug ear plugs) have an advantage here: the graduated flanges create a seal at multiple points in the ear canal, so even if insertion is not perfect, you still get meaningful protection. This is one reason flanged plugs tend to perform closer to their rated NRR in real-world use compared to foam plugs that require precise rolling and insertion technique.

Frequently Asked Questions

Is a higher NRR always safer?

Not necessarily. You need enough protection to bring your exposure below 85 dB, but too much can prevent you from hearing important sounds like alarms, equipment warnings, or coworker communication. Match the NRR to your noise environment.

Do I add the NRR numbers together if I wear plugs and earmuffs?

No. Take the higher NRR of the two devices and add 5 dB. That is your combined effective NRR.

How often should I replace my ear plugs?

Disposable foam plugs are single-use. Reusable silicone or TPR plugs (like PermaPlug) last weeks to months with regular cleaning. Replace them when the material loses its flexibility or no longer creates a snug seal.

Can I use the same ear plugs for shooting and construction?

Yes, as long as the NRR is adequate for both environments. Gunshots produce 140-170 dB, which is extreme. NRR 27-33 ear plugs will help, but serious shooters often double up with plugs plus earmuffs.

What is the minimum NRR required by OSHA?

OSHA does not specify a minimum NRR. Instead, OSHA requires that the hearing protection you provide reduces worker exposure below 90 dB (or 85 dB for workers already in a hearing conservation program). The NRR you need depends on the noise level of your specific work environment.

What does “NRR 27 dB” mean in practical terms?

Under laboratory conditions, the device reduces noise by 27 decibels. In real-world use, OSHA estimates the actual reduction at about 10 dB using their derating formula. With proper fit technique, your actual protection will fall somewhere between those two numbers.