Hearing safety · hearing protection
Earplug NRR real-world calculator.
Enter the NRR on the package and the noise level in dBA. See the estimated level under the protector by the OSHA Appendix B method, the OSHA 50% derating and the NIOSH derating for your protector type.
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Result
Enter the NRR and the noise level.
NRR on the label versus real-world protection
The NRR (Noise Reduction Rating) is a laboratory number that US EPA regulation requires on the package. People rarely get lab-quality fit, so both agencies adjust it. For an A-weighted noise level, OSHA Appendix B subtracts 7 dB from the NRR, so the effective level is dBA - (NRR - 7). That is OSHA's Appendix B method. NIOSH adds a type-specific derating first: subtract 25% from the NRR for earmuffs, 50% for slow-recovery formable earplugs and 70% for all other earplugs, then use ENL = dBA - (derated NRR - 7). OSHA has also instructed its inspectors to derate the NRR by 50% when enforcing the engineering-controls provision.
Worked example, earplug. A foam earplug with NRR 33 in 100 dBA noise. Appendix B gives 100 - (33 - 7) = 74 dBA. OSHA's 50% derating gives 100 - (33 - 7) x 50% = 87.0 dBA. NIOSH's 70% derating leaves an NRR of 9.9, so the level is 100 - (9.9 - 7) = 97.1 dBA: the real-world reduction might be only 2.9 dB, not 26.
Worked example, earmuff. NRR 25 in 95 dBA: the NIOSH 25% derating gives 18.75, so the level is 83.25 dBA. The page floors protection at 0 dB when the derated NRR is under 7.
NIOSH itself says fit testing, which produces a Personal Attenuation Rating, is the best way to check protection, and that the NRR "often does not reflect the actual protection provided for each worker". NIOSH's text gives 70% for all other earplugs in its formal recommendation and summary but 75% in one discussion passage; this page uses 70%. A 75% derate would give a slightly lower real-world reduction.
Frequently asked questions
Why is the real protection lower than the NRR?
The NRR comes from laboratory tests with ideal fit. In real use fit, insertion depth, wear and other gear reduce it, so NIOSH recommends subtracting 25% for earmuffs, 50% for formable earplugs and 70% for other earplugs.
Why subtract 7 dB?
The NRR is meant to be subtracted from a C-weighted level. For an A-weighted reading, OSHA Appendix B and NIOSH both subtract 7 dB from the NRR first.
Can I add the NRRs of earplugs and earmuffs together?
No. Wearing both does not add the two ratings. NIOSH recommends double protection above a 100 dBA 8-hour average but gives no addition rule.
Is this a replacement for a fit test?
No. NIOSH says individual fit testing is the best way to check protection. This tool is a planning estimate.
Sources
Checked
- NIOSH 98-126: Criteria for a Recommended Standard, Occupational Noise Exposure, Revised Criteria 1998
- CDC NIOSH: Provide Hearing Protection
- OSHA 1910.95 Appendix B: Methods for estimating the adequacy of hearing protector attenuation
- OSHA Technical Manual, Section III Chapter 5: Noise (Appendix F, 50% derating)
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Hearing safety guidance, not medical or occupational-health advice. These are published limits and rules of thumb applied as arithmetic, not a noise survey. Measure real levels with a sound level meter or dosimeter, follow the rules that apply to your workplace, and see an audiologist if you have ringing, muffled hearing or hearing loss.