Noise Reduction Rating Explained

NRR Feature Image
NRR Feature Image

We independently review all our recommendations. Purchases made via our links may earn us a commission. Learn more ❯

Understand the basics and importance of Noise Reduction Ratings (NRR) to protect your hearing.

Noise Reduction Rating (NRR) is one of the principal factors users look for when hunting for Hearing Protection Devices (HPDs).

Unfortunately, understanding the NRR of HPDs can be complex, as it’s not always clear how much noise they’ll reduce in real-world situations.

This article goes over the measurements and calculations that will help you understand what the NRR on hearing protection really means when it comes to the amount of noise it reduces. Let’s get started!

What Is Noise Reduction Rating (NRR)?

Noise Reduction Rating (NRR) label for hearing protection devices
Noise Reduction Rating (NRR) label for hearing protection devices

A Noise Reduction Rating indicates a hearing protection device’s ability to reduce the noise level coming into the user’s ears from external surroundings.

It is the official standard for attenuation in the USA and serves as a reference point for buyers looking for HPDs. The rating shows how effectively a device attenuates external noise. The higher the rating, the more effectively the HPD will reduce noise exposure.

Any hearing protection device (HPD) manufactured after 1979 must provide its NRR on a label.

An HPD with an NRR of 31 can ideally reduce noise by 31 decibels (dB) in controlled lab conditions. However, as we’ll explore in later sections, NRR and actual noise reduction don’t maintain a 1:1 relationship in everyday situations.

How Much Noise Reduction Do You Need?

Before getting into how much noise reduction an HPD with a given NRR will actually provide, you might want to first figure out how much noise reduction you need in the first place.

According to the U.S. CDC, approximately 22 million Americans are exposed to hazardous noise at the workplace each year. What’s more, Apple Watch data indicates that as many as one in three Americans are exposed to noise levels above 70 dB.

For a quick reference, here’s breakdown of the time and dBA thresholds for excessive noise according to OSHA and NIOSH:

Maximum duration per dayExcessive noise threshold per NIOSH RELExcessive noise threshold per OSHA PEL
8 hours85 dBA90 dBA
4 hours88 dBA95 dBA
2 hours91 dBA100 dBA
1 hour94 dBA105 dBA
30 minutes97 dBA110 dBA
15 minutes100 dBA115 dBA

Thankfully, measuring noise levels is pretty easy. Decibel meters, also called sound pressure level (SPL) meters, are simple and inexpensive devices that will measure the noise level of your environment in dBA. You can also use an app to measure noise levels if you’re trying to keep things as simple as possible.

Once you have measured the noise levels to which you’re exposed, subtract 85 to 90 dBA from the reading on your SPL meter/app. The number you’re left with is the minimum amount of noise reduction in dBA that you’ll need for 8 hours of safe noise exposure, as per the above table.

We’ll be focusing on the A-weighted decibel scale (dBA) in this article rather than the C-weighted decibel scale (dBC).

How to Calculate Actual Noise Reduction Based on NRR

NRR is the critical variable in calculating the amount of noise an HPD will reduce in a real-world setting. As mentioned earlier, the NRR on an HPD can’t be taken at face value as it only indicates the number of decibels the device can attenuate under ideal lab conditions.

Below are different ways to calculate the amount of real noise reduction provided by an HPD by using its NRR according to OSHA and NIOSH’s derating formulas.

Calculating noise reduction based on NRR: OSHA method

The U.S. OSHA’s (Occupational Safety and Health Administration) method of calculating the total noise reduction of and HPD in dBA based on NRR is as follows:

(NRR – 7)*0.5 = Amount of noise reduction (dBA)

Let’s apply the formula by using an example of an HPD with an NRR of 28. To find how much noise it will reduce in dBA, we would do the following:

(28 – 7)*0.5 = 10.5 dBA of noise reduction.

So, based on the OSHA method of calculating noise reduction, we can say that an HPD with an NRR of 28 will reduce noise by 10.5 dBA.

Calculating noise reduction based on NRR: NIOSH method

The U.S. NIOSH (National Institute for Occupational Safety and Health) method differs slightly from the OSHA method. Most importantly, it considers the type of HPD in use.

The NIOSH method for calculating noise reduction in dBA based on an HPD’s NRR is as follows:

Ear muffs: [NRR-(NRR*0.25)]-7 = Amount of noise reduction (dBA)

Formable earplugs:[NRR-(NRR*0.5)]-7= Amount of noise reduction (dBA)

All other earplugs: [NRR-(NRR*0.7)]-7= Amount of noise reduction (dBA)

Let’s use an example of an HPD with an NRR of 28 and apply the NIOSH method. We’ll also say that the HPD in question is a pair of earmuffs. We can calculate the amount of noise reduced in dBA according to NIOSH with the following calculation:

[28-(28 * .25)]-7= 14 dBA of noise reduction

Single Number Rating (SNR) vs NRR: What’s the Difference?

While the NRR is the standard for hearing protection attenuation across North America, the Single Number Rating (SNR) is the EU standard. The main difference between SNR and NRR is that the former’s ratings are typically a few decibels higher due to different lab testing procedures.

There is currently no exact formula to convert NRR rating values to SNR or vice versa.

Like NRR, SNR provides an estimate of an HPD’s level of noise reduction in controlled lab conditions. Calculating the real amount of noise reduction in dBA that an HPD can provide by using SNR varies from country to country. The UK, however, uses the most simple and straightfoward calculation:

SNR-4=Amount of noise reduction

SNR is frequently paired with HML values, which indicate whether an HPD is most effective at attenuating high, medium, or low-frequency sounds (indicated with an H, M, or L, respectively).

Frequently Asked Questions

Can you improve the amount of noise reduction provided by hearing protection devices?

Yes. Dual noise protection, or wearing two sets of hearing protection devices (earmuffs on top of earplugs, for example), can improve noise reduction anywhere from -4 to -8dB when compared to wearing just one HPD.

Which hearing protection devices have the highest NRR?

The highest NRR for in-ear protection is around 33, and is usually found in formable earplugs, like 3M’s Uncorded, Disposable, Foam Earplugs since they adapt better to the users’ ear shape. On the other hand, the highest NRR for on-ear protection like earmuffs is 31, as is the case with the 3M Peltor X5A.

How are noise reduction ratings tested and determined?

Entities that manufacture and sell HPDs must test the same in a testing facility that complies with the EPA’s regulations. Consequently, they must test the device on ten different trained human subjects under anechoic conditions, using 9 test frequencies.

Who came up with NRR?

The U.S. Environmental Protection Agency (EPA) came up with the definition of NRR in the 1970s, under their Noise Label Program.

Can I listen to music with hearing protection devices?

Many HPD’s do in fact double as headphones, such as the PRO 037 – just one example of many.

💬 Conversation: 5 comments

  1. I’ve been looking for appropriate ear plugs for motorcycle use. I’ve gravitated towards those offered to the european market, especially those with a stated SNR. I prefer the SNR because usually low, medium, and high frequency attenuations are available for the product or included in instructions. On a motorcycle, there is usually a cacophony which varies greatly depending on conditions. Some of these are good to hear and some not so good, especially on a motorcycle. In calculating the derated SNR for an earplug with an included list of various frequency attenuations, can the -4 derated value be applied to all or certain frequencies listed, or does this derated value only apply to the stated SNR and not a certain frequency?

  2. Appreciate Chief Editor’s introduction. This information is very useful. Look forward to seeing some introduction about the measuring process of SNR and NRR!

  3. Products like Alpine SleepDeep claim to provide the maximum noise attenuation possible – 27 dB. Cheap foam earplugs (“disposable”, but seem reusable to me) have an NRR of 33 (dB). Is the cheapest product better than the “maximum”, or am I being confused / misled by two different rating systems?

    I have no need to hear anything thru the noise reducers – I’m not on a work site or at a concert. I’m not seeking hearing protection.

    I’m desperate to sleep. Footsteps from the apartment above me (in an old house) combine thud and creak. Also traffic noise. There is carpet (old) on the floor above which might reduce click clack noise, but seems to have zero effect otherwise.

    I am interested in combining earplugs and earmuffs, preferably where rolling on my side won’t cause the earmuffs to physically wake me

    I wonder if active noise cancelling headphones will help.

    Thanks for the most comprehensive article on noise ratings. Somehow I couldn’t quite apply it to understand what would be a good solution to my needs. Help?

  4. Seems the bottom line is that the decibel rating of a headset is essentially meaningless. You have to do a bunch of math to figure out how much hearing protection you’re really getting? Why don’t they come up with a rating system that just gives the actual rating of the device? I guess my rule of thumb from here on out will be, Pick the highest decibel rating you can get, and it’s not as high as you think.

Leave a Reply