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Direct comparison
NRR vs SNR: How Earplug Ratings Are Used
NRR vs SNR for hearing protection: what each stands for, how OSHA applies NRR and HSE uses SNR bands, and why neither number can be converted.
Written and maintained by CASRAI Editorial Board
Last updated
How do NRR (Noise Reduction Rating) and SNR (Single Number Rating) compare side by side?
The table below compares NRR (Noise Reduction Rating) and SNR (Single Number Rating) across 11 dimensions, from what it stands for to when to pick each.
Side-by-side comparison
| Dimension | NRR (Noise Reduction Rating) | SNR (Single Number Rating) |
|---|---|---|
| What it stands for | Noise Reduction Rating. OSHA describes it as the rating developed by the US Environmental Protection Agency (EPA). | Single Number Rating. HSE describes it as the value provided with a hearing protection device. |
| Where the sources use it | EPA hearing protector labelling rules (40 CFR Part 211) and OSHA 29 CFR 1910.95 Appendix B. | HSE guidance on choosing hearing protection and avoiding over-protection (Great Britain). |
| What the number is | A single-number noise reduction factor in decibels. The EPA rule ties it to the test method ANSI S3.19-1974. | A single decibel value supplied with the protector, used with HSE's indicative table. |
| Label wording | The EPA label carries "(When used as directed)", and the labelled NRR may not exceed the computed value. | Not stated on the HSE pages read for this page. |
| How the number is applied | OSHA: with a C-weighted noise level, subtract the NRR from it. With an A-weighted level, subtract 7 dB from the NRR first, then subtract the remainder from the A-weighted level. | HSE: find the A-weighted noise level during the task in an indicative table and choose a protector whose SNR falls in the matching band. |
| Indicative bands | None. The method is subtraction, not a table of bands. | HSE table (A-weighted level to SNR): 85-90 dB, SNR 20 or less; 90-95 dB, 20-30; 95-100 dB, 25-35; 100-105 dB, 30 or more. |
| Over-protection | The Appendix B calculation does not include a lower limit. | HSE says protectors that reduce the level at the ear to below 70 dB should be avoided, and aims at least to get below 85 dB at the ear. |
| When the method does not fit | OSHA notes calculated values reflect realistic values only to the extent that protectors are properly fitted and worn. | HSE calls its table a guide, not a substitute for a standardised calculation method, and not appropriate if the noise has significant low-frequency components (for example press shops, plant rooms, boiler houses, punch presses). |
| Fit and real-world performance | A CDC-hosted study of four earplugs (Franks et al., 2000) found the fit-tested rating NRR(SF) is typically lower than the labelled NRR. | HSE bases its guidance on the SNR provided with the device; it does not claim the figure reflects any individual's fit. |
| Converting between them | No source read gives a conversion formula. Do not subtract or add a fixed number to turn an NRR into an SNR. | Same: use the SNR with HSE's table, not an NRR-derived estimate. |
| When to pick each | Use the NRR method when the label gives an NRR and a US workplace rule (OSHA) governs the exposure calculation. | Use the SNR table when the protector gives an SNR and the workplace is in Great Britain under HSE guidance. |
Sources
- OSHA 29 CFR 1910.95 Appendix B (https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.95AppB)
- 40 CFR 211.203 and 211.204-1
- Franks et al. 2000, Ear and Hearing 21(3):218-226 (https://stacks.cdc.gov/view/cdc/198354). Read 2026-10-30
- HSE, Hearing protection (https://www.hse.gov.uk/noise/hearingprotection.htm) and Over-protection (https://www.hse.gov.uk/noise/goodpractice/hearingoverprotection.htm). Read 2026-10-30
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Common questions
Common questions about NRR (Noise Reduction Rating) vs SNR (Single Number Rating)
What does NRR stand for in ear plugs?
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NRR stands for Noise Reduction Rating. OSHA describes it as the rating developed by the US EPA, and the EPA defines it in 40 CFR 211.203 as a single-number noise reduction factor in decibels. The label says "(When used as directed)", so it describes the protector used as directed, not every wearer's fit.
What does SNR stand for?
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SNR stands for Single Number Rating. HSE's guidance on hearing protection says its method is based on the SNR value provided with a hearing protection device.
Is NRR 22 good enough for shooting?
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No NRR figure is a pass mark on its own. OSHA's method turns an NRR into an estimated level at the ear: with an A-weighted level it subtracts 7 dB from the NRR first, so an NRR of 22 leaves a 15 dB correction. For example, 100 dB A-weighted minus 15 dB gives 85 dB (an illustrative calculation, not a recommendation). OSHA also notes the result is realistic only when protectors are fitted and worn properly, and a CDC-hosted study found fit-tested ratings are typically lower than labelled NRRs. Whether that is enough depends on the noise actually present at the ear.
Can you convert NRR to SNR?
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Not from the sources read here. OSHA gives a method for using an NRR and HSE gives a table for using an SNR; neither source gives a formula that converts one number into the other.
Can a protector reduce noise too much?
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Yes. HSE advises avoiding protectors that reduce the level at the ear to below 70 dB, and its table is meant to help pick an SNR that avoids over-protection.
Going deeper
