SLC80 vs NRR: How Australian and US Hearing Ratings Differ
SLC80 is the rating Australian workplaces use. NRR is the US rating. Both are decibel figures printed on hearing protectors, but they come from different test methods and different maths, so you cannot swap one for the other or convert between them with a simple formula. If you buy for an Australian site, the protector needs to be tested to AS/NZS 1270 and selected using its SLC80 or Class. An NRR on its own does not meet that requirement.
This guide explains what each number means, why they differ, how to use the Australian system on a real site, and why the printed rating is only the start of knowing whether a worker is actually protected.
TL;DR
SLC80 (Sound Level Conversion, 80th percentile) is the Australian and New Zealand rating under AS/NZS 1270. It predicts the protection achieved by 80% of users.
NRR (Noise Reduction Rating) is the US system. NSW’s regulator says it is not acceptable in Australia because its testing method differs from AS/NZS 1270:2001.
The two use different statistical corrections and inputs, so the numbers are not directly comparable. Do not subtract, add or convert them.
A higher rating is not automatically better. Over-protection can stop workers hearing instructions and warnings.
Group ratings do not tell you what one person gets. An individual fit test does.
Table of Contents
What SLC80 and NRR actually measure
Both ratings try to answer the same question: how much quieter does this protector make the noise at the wearer’s ear? They answer it with different laboratory procedures and different calculations.
SLC80 in Australia and New Zealand
SLC80 is specified in AS/NZS 1270 and is intended to predict the protection achieved by 80% of users. Put plainly, if a protector has an SLC80 of 20 dB, about four in five wearers should get at least that much reduction when it is fitted properly. One in five may get less.
The figure is tied to the way noise is measured on site. WorkSafe Queensland explains that SLC80 is the difference between the measured C-weighted noise level in the workplace and the target A-weighted noise level at the ear. That is why it works neatly with a sound level meter reading taken on your site.
NRR in the United States
NRR is the US rating. It also expresses an expected reduction in decibels, but it is derived under a different test method. Historically it applies a two-standard-deviation correction and a 3 dB spectral safety factor, whereas SLC80 uses a one-standard-deviation correction. The result is a number built for US regulations, not Australian ones.
You will see NRR on packaging when products are imported or bought from overseas suppliers. It is a perfectly valid figure in the market it was designed for. The problem is only using it where the standard asks for something else.
The short comparison
SLC80 | NRR | |
Region | Australia and New Zealand | United States |
Standard | AS/NZS 1270 | US testing method |
Meaning | Reduction expected for 80% of users | Average-based estimate with a 2-SD correction |
Statistical correction | 1 standard deviation | 2 standard deviations plus 3 dB safety factor |
Accepted for Australian workplace selection | Yes | No |
Used with Australian classes (1 to 5) | Yes | No |
Can you convert NRR to SLC80?
No. This is the question that trips up most buyers, and the honest answer is that there is no reliable conversion. Ratings such as NRR, the European SNR and SLC80 are not directly comparable because the testing protocols, calculation methods and required data inputs all differ.
You may see rules of thumb online, such as subtracting a fixed number of decibels from an NRR. Treat these as rough marketing shorthand. They can overstate or understate protection, and they do not make an unrated product compliant.
There is one useful point of perspective. Acoustics Australia researchers noted that despite different standards (AS/NZS, ANSI, ISO), the underlying idea of testing is similar: ratings are based on a person’s hearing thresholds with and without the protector in place. The details and the final reporting differ, and those details are exactly why you cannot convert.
What the Australian rules ask for
The Safe Work Australia model code of practice on managing noise is the reference most state and territory regulators build on. It says hearing protectors must be selected and maintained in line with AS/NZS 1269.3:2005, and that attenuation values must come from testing to AS/NZS 1270, as set out in the Managing noise and preventing hearing loss at work code of practice.
In practice, that means three things for a manager:
Buy protectors that are tested and labelled to AS/NZS 1270.
Choose them based on the measured noise exposure for the job, not on the biggest number available.
Keep them fitted, maintained and replaced as part of a hearing protector program.
A note for readers outside Western Australia: the model code is a national template, and each jurisdiction applies its own regulations and codes. Check your own regulator for the exact wording that applies on your site.
Using SLC80 and the Class system
AS/NZS 1269.3 describes three main selection methods: the octave band method, the SLC80 method and the classification method. WorkSafe Victoria lists all three and notes that the Class, SLC80 value and octave data are usually on the packaging or the protector itself.
For most sites, the classification method is the quickest. The Safe Work Australia code directs workers and managers to use the Class system (Classes 1 to 5) based on the measured eight-hour exposure level, LAeq,8h. Each Class covers a band of SLC80 values:
Class | SLC80 range |
Class 1 | 10 to 13 dB |
Class 2 | 14 to 17 dB |
Class 3 | 18 to 21 dB |
Class 4 | 22 to 25 dB |
Class 5 | 26 dB and above |
The relationship between Class and SLC80 is set out in the Victorian regulator’s guidance, and the matching exposure levels for each Class are in AS/NZS 1269.3 and the model code. Take your noise assessment, find the Class that brings the exposure down to an acceptable level at the ear, then check it against comfort, communication and the other equipment your people wear.
A worked example
Say a crew works near a compressor and a generator, and your noise assessment gives an eight-hour exposure that calls for a Class 3 protector. You compare two earmuffs. One is labelled Class 3 to AS/NZS 1270. The other is an imported pair labelled with a higher NRR but no Australian class. The first can be selected with confidence using your assessment. The second cannot be placed on the Australian scale at all, however impressive its number looks.
Does a higher rating mean better protection?
No. More attenuation is not always safer. The Safe Work Australia code warns about over-protection: protectors should be chosen so they do not cut out so much sound that workers cannot hear verbal instructions or safety-related sounds. Workers who feel isolated tend to lift or remove protectors, and then they are exposed to the full noise.
WorkSafe Queensland gives a practical target. It recommends that noise at the ear should generally fall between 75 and 80 dB(A), and treats reduction to below 70 dB(A) as over-protection.
There is a second catch. The same guidance notes that standard industrial protectors can over-attenuate the higher frequencies that carry speech, which distorts communication. Where that is a problem, flat-attenuating protectors may be the right choice. They lower the volume more evenly across frequencies so speech stays clearer.
So the selection question is not “what is the highest Class?” It is “what is the lowest Class that brings this person’s exposure into the safe range, and that they will actually keep on?”
Earplugs and earmuffs together
Yes, you can wear them together, and in some situations you must. The Safe Work Australia code requires combination protection for high-impulse noise such as blasting or large-calibre weapons: well-fitted earplugs of at least Class 3 plus earmuffs.
Do not add the two ratings. Combined protection is not a simple sum, because sound also reaches the inner ear through bone and through the gaps around the devices. The combined setup needs to be assessed as part of your overall hearing protector program.
Why the printed rating is not what your worker gets
SLC80, NRR and SNR are statistical estimates for groups of people tested in a lab. Without individual fit-test data, they are not reliable indicators of what a particular wearer receives. Two workers using the same earplug can have very different results.
Fit varies for ordinary reasons:
Ear canal shape and size. One earplug size does not suit everyone.
Insertion technique. Roll, reach over the head, pull the ear up and back, hold. Many people skip steps.
Other equipment. Safe Work Australia notes that spectacles, hard hats and dust masks can significantly affect the performance and fit of hearing protectors. Earmuff seals break around glasses arms and respirator straps.
Wear and tear. Cushions harden, foam plugs lose shape, and headbands loosen.
This is why a Class 4 label does not guarantee Class 4 protection on a given head. It tells you the product was tested properly. It does not tell you the product is fitted properly.
What a fit test adds
A hearing protector fit test measures the attenuation a specific person achieves with a specific protector. It turns a group estimate into an individual result, so you can see who is under-protected and fix it on the spot with a different size, a different model or a quick coaching session.
Our own guides go deeper on the practical side:
Fit tests for safety managers take around 5 to 10 minutes per person.
Three earplug fit testing methods explain how results can lift personal attenuation.
Choosing an earplug size covers when a home tug test is not enough.
Retest timing and retesting at onboarding and after changes show when to repeat the test.
Audit-ready hearing conservation with mobile fit testing shows how the records fit into a compliance program.
Our perspective
We deliver training and fit testing to businesses across the Pilbara, including remote mine and construction sites, and the same pattern turns up often: a store of hearing protectors bought on price or on the biggest number, and a workforce that has never been checked to see whether any of it fits.
Our view is simple. The label gets the product into the conversation. The fit test tells you whether the worker is protected. Treat SLC80 and Class as the way you shortlist products that suit your measured noise levels, then confirm the result on the people who wear them. Pay attention to the whole kit, too: if your crews wear glasses, hard hats and respirators, test the protector with all of it on.
We would rather your team be properly fitted in a Class 3 protector they keep in than issued a Class 5 they push up off their ears. Over-protection and poor fit are both preventable, and neither is solved by chasing a number.
— Vapour
Getting your team fit tested
We bring hearing protective device fit testing to your site, with flexible scheduling outside standard business hours, so crews do not lose production time. Our trainers have industry-relevant experience and we can tailor the session to the protectors and noise environment you actually have. Fit test pricing is not published, so get in touch for a quote through our hearing protective device fit test page. You can also browse the full list of site safety courses and fit tests.
If your sites are remote, our HLTAID013 Provide First Aid in Remote or Isolated Site course is $400 and is built for exactly those conditions.
A quick checklist for buying and issuing protectors
Get a current noise assessment so you know the eight-hour exposure for each role.
Choose protectors labelled to AS/NZS 1270 with a Class that suits the exposure, not just the highest available.
Check communication needs. Where speech and alarms matter, consider flat-attenuating options.
Check compatibility with helmets, glasses and respirators.
Offer more than one model and size.
Fit test each worker with their chosen protector and record the result.
Retest after changes in equipment, role or health, and review regularly.
FAQ
What does SLC80 mean?
SLC80 stands for Sound Level Conversion at the 80th percentile. It is the rating defined in AS/NZS 1270 and it predicts the level of protection that 80% of wearers should achieve when the protector is correctly fitted. Australian Classes 1 to 5 are built from SLC80 values.
Is a higher NRR or SLC80 always better?
No. Too much attenuation can make it hard to hear instructions and warnings, and workers may then remove their protectors. Safe Work Australia advises choosing protectors that avoid over-protection. Aim for the lowest Class that brings the noise at the ear into a safe range for the job.
Can I wear earmuffs and earplugs together?
Yes. For high-impulse noise such as blasting, the Safe Work Australia code requires well-fitted earplugs of at least Class 3 plus earmuffs. The combined protection is not the sum of the two ratings, so the combination should be assessed within your hearing protector program.
Can I use NRR-rated earplugs on an Australian site?
NRR on its own is not acceptable under Australian requirements, because the testing method differs from AS/NZS 1270. Choose products tested and labelled to the Australian standard, and confirm fit on the individual wearer.
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