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Hearing Protector NRR Derating Calculator

Enter the measured noise level and the protector's labeled NRR to get the estimated exposure under the hearing protector. The calculator applies the 29 CFR 1910.95 Appendix B methods, OSHA's 50% safety factor and the NIOSH 1998 derating by protector type, and compares each result to the 90 dBA PEL and the 85 dBA limits.

dB
Use the dBA or dBC value that matches the method below.
dB
Printed on the package, from the EPA label (ANSI S3.19 lab test).
OSHA: 5 dB can be added to the NRR of the most protective device when both are worn.

Results are estimates for planning purposes and do not replace a competent person's evaluation or an engineer's design. Follow the OSHA standards that apply to your work and your employer's written program.

The limits your result is compared to

Level (8-hour TWA)What it isReference
90 dBAOSHA permissible exposure limit (PEL)29 CFR 1910.95(a)
85 dBAOSHA action level — hearing conservation program, audiometric testing29 CFR 1910.95(c)
85 dBANIOSH recommended exposure limit (REL), 3 dB exchange rateNIOSH 98-126

Over-protection is a real hazard too: attenuation that drops speech and backup alarms below what a worker can hear leads to protectors being pulled out. Pick the protector that brings the exposure to the target, not the highest NRR on the shelf.

Derating is a stopgap — fit testing is the current NIOSH recommendation

The NRR comes from a laboratory fit under ANSI S3.19, which is why every method on this page cuts it down. NIOSH's 2025 science policy update supersedes the 1998 derating guidance and recommends quantitative, individual fit testing: each worker gets a measured personal attenuation rating (PAR) for the protector they actually wear. Use the derated numbers here for planning and protector selection, and a fit-test PAR when you have one.

How it's calculated

OSHA Appendix B — A-weighted noise measurement
Estimated exposure under the protector (dBA) = TWA (dBA) − (NRR − 7)
Subtract 7 dB from the NRR, then subtract the remainder from the A-weighted TWA.
OSHA Appendix B — C-weighted noise measurement
Estimated exposure under the protector (dBA) = TWA (dBC) − NRR
No 7 dB correction: the NRR is subtracted directly from the C-weighted level.
OSHA 50% safety factor (derated NRR)
Estimated exposure (dBA) = TWA (dBA) − (NRR − 7) / 2
OSHA compliance personnel apply a 50% safety factor to the laboratory NRR, above and beyond the 7 dB subtraction, when considering whether engineering controls are required. It is not used to evaluate the adequacy of hearing protectors under the hearing conservation program.
NIOSH 1998 derating by protector type
derated NRR = NRR × (1 − f), with f = 25% earmuffs, 50% formable earplugs, 70% all other earplugs; exposure (dBA) = TWA (dBA) − (derated NRR − 7)
NIOSH applies the derated NRR to a C-weighted level directly, or the derated NRR minus 7 dB to an A-weighted level. NIOSH's 2025 science policy update supersedes this derating guidance and recommends individual fit testing instead.
Dual protection (earplugs + earmuffs)
NRR used = NRR of the more protective device + 5 dB
The two devices are not additive. This calculator adds the 5 dB to the labeled NRR before derating, which is the more conservative reading.

Frequently asked questions

Not 33 dB. Under 29 CFR 1910.95 Appendix B you subtract 7 dB from the NRR before applying it to an A-weighted level, so NRR 33 gives 26 dB. With OSHA's 50% safety factor, (33 − 7) / 2 = 13 dB. The NRR comes from a laboratory fit that workers rarely reproduce on the job.

The NRR is derived from C-weighted laboratory data. When your measurement is A-weighted, Appendix B directs you to subtract 7 dB from the NRR to account for the spectral difference. If you measure a C-weighted TWA, you subtract the NRR directly with no 7 dB correction.

OSHA compliance officers apply the 50% safety factor when deciding whether an employer must install engineering controls. OSHA's 2021 interpretation states that the safety factor is not used when evaluating whether hearing protectors are adequate under the hearing conservation program.

The 1998 NIOSH criteria document derates the labeled NRR by 25% for earmuffs, 50% for slow-recovery formable earplugs and 70% for all other earplugs. The derated NRR is subtracted from a C-weighted level, or the derated NRR minus 7 dB from an A-weighted level.

No. Attenuation is not additive because the bone-conduction path limits the total. OSHA's guidance is to add 5 dB to the NRR of the more protective of the two devices, then apply the usual method.

The OSHA permissible exposure limit is a 90 dBA 8-hour TWA (29 CFR 1910.95(a)), the hearing conservation action level is 85 dBA, and the NIOSH recommended exposure limit is 85 dBA. Over-protecting also has a cost: too much attenuation makes speech and backup alarms hard to hear.

NIOSH now recommends individual, quantitative fit testing instead. Its 2025 science policy update supersedes the 1998 derating guidance and points employers to a measured personal attenuation rating for each worker and protector.

Sources & references

Content checked against these sources — last reviewed August 27, 2026.

By — Editorial team of SteelToeTools.com (published by LSEA SAS) Updated v1