NRR vs SNR: what earplug ratings really mean

NRR (US)

The Noise Reduction Rating is measured in a lab with trained listeners and a careful fit, and is stated against C-weighted levels. Real-world wearers get much less. NIOSH recommends derating the label by type: subtract 25% for earmuffs, 50% for foam earplugs and 70% for other earplugs. OSHA’s guidance subtracts 7 dB when the noise was measured in dBA, and halves the result when judging how well protectors work in practice¹.

At 100 dBA, wearing	NIOSH estimate at the ear	OSHA field estimate at the ear
Foam earplugs, NRR 33	90.5 dBA	87 dBA
Pre-moulded earplugs, NRR 25	99.5 dBA	91 dBA
Earmuffs, NRR 25	88.3 dBA	91 dBA

NIOSH: L − (NRR × (1 − derating) − 7). OSHA: L − (NRR − 7) ÷ 2. Calculated by the same code as the noise dose calculator.

SNR (UK and EU)

The Single Number Rating comes from the European test standard (EN 352 and ISO 4869). Subtract it from the C-weighted noise level to estimate the A-weighted level at the ear. HSE advises allowing for real-world fit by reducing the protection by 4 dB². The H, M and L values on the pack give a better estimate when the noise is mostly high, medium or low pitched.

Aim for enough, not the most

More attenuation is not always better. HSE advises choosing protection that gets the level at the ear below 85 dB, but avoiding protectors that take it below 70 dB, because over-protection makes speech and warning signals hard to hear². People also take uncomfortable, over-strong protection out, and protection worn half the time is worth little.

Fit is everything

Foam plugs: roll into a thin crease-free cylinder, pull the ear up and back, insert, hold for 20 to 30 seconds while it expands.
Earmuffs: hair, glasses arms and hats under the seal reduce protection.
Check: with plugs in, your own voice should sound louder and deeper, and outside noise clearly muffled.

Questions

Is a higher NRR always better?

Not necessarily. Most people get far less than the label in practice, and too much attenuation can make you remove protection. Fit and wearing time matter more.

How do I convert SNR to NRR?

There is no exact conversion; the tests differ. As a rough guide SNR values run a few decibels higher than NRR for the same product.

Sources

The NRR is meant to be subtracted from a C-weighted level. With an A-weighted level, subtract 7 dB from the NRR first. OSHA then halves the result (a 50% safety factor) when judging engineering controls: protected level = dBA - (NRR - 7) / 2. NIOSH instead derates the labelled NRR by type (earmuffs -25%, formable earplugs -50%, all other earplugs -70%) and then applies the 7 dB: protected level = dBA - (derated NRR - 7).
- 29 CFR 1910.95 Occupational noise exposure (Code of Federal Regulations, 2024 edition), Appendix B, U.S. Government Publishing Office (govinfo.gov).(B) Subtract 7 dB from the NRR, and subtract the remainder from the A-weighted TWA to obtain the estimated A-weighted TWA under the ear protector.(B) Subtract the NRR from the C-weighted TWA to obtain the estimated A-weighted TWA under the ear protector.Checked 2026-11-02.
- Criteria for a Recommended Standard: Occupational Noise Exposure, Revised Criteria 1998 (DHHS (NIOSH) Publication No. 98-126), NIOSH / CDC (CDC Stacks).In calculating the noise exposure to the wearer of a hearing protector at work, OSHA derates the NRR by one-half for all types of hearing protectors.OSHA [1983] has instructed its compliance officers to derate the NRR by 50% in enforcing the engineering control provision of the OSHA noise standard.NIOSH recommends derating by subtracting from the NRR 25%, 50%, and 70% for earmuffs, formable earplugs, and all other earplugs, respectively.All other earplugs Subtract 75% from the manufacturer’s labeled NRRENL = dBA – (derated NRR-7)ENL = dBC – derated NRRIt is important to note that when working with A-weighted noise levels, one must subtract an additional 7 dB from the labeled NRR to obtain an estimate of the A-weighted noise level under the protector.Checked 2026-11-02.
In Europe protectors carry an SNR (and H, M, L values) under EN ISO 4869-2. The protected A-weighted level is L'A = LC - SNR, using a C-weighted measurement. HSE recommends adding 4 dB to the calculated L'A as a real-world factor (not for peak noise). If you only have A-weighted levels, HSE's table suggests an SNR of 20 or less for 85-90 dB(A), 20-30 for 90-95, 25-35 for 95-100 and 30 or more for 100-105, and it advises against reducing the level at the ear below 70 dB.
- Controlling noise at work. The Control of Noise at Work Regulations 2005. Guidance on Regulations (L108), Health and Safety Executive (HSE).L’A = LC – SNRThe effective A-weighted sound pressure level at the ear, L’A , is given by subtracting the SNR value for the protector from the C-weighted sound pressure level LC:HSE recommends that 4 dB be regarded as an appropriate factor to bridge the gap between manufacturers’ data and real-world factors.22 To account for real-world factors, add 4 dB to the calculated L’A in order to give a more realistic estimate for the protected level at the ear.This adjustment for real-world protection should not be applied to the assessment of hearing protector performance against peak noise.The HML method requires measurement of the A-weighted (L A ) and C-weighted (LC) sound pressure levels.(d) single number rating (SNR) value in accordance with BS EN ISO 4869-2.will be no more than 6 dB over that of the higher SNRChecked 2026-11-02.
- Noise at work: Hearing protection, Health and Safety Executive (HSE).A-weighted noise level (dB) Select a protector with the right SNR 85 to 90 20 or less 90 to 95 20 to 30 95 to 100 25 to 35 100 to 105 30 or moremake sure the protectors give enough protection - aim at least to get below 85 dB at the earProtectors that reduce the level at the ear to below 70 dB should be avoided, since this over-protection may cause difficulties with communication and hearing warning signals.Checked 2026-11-02.

General information, not medical advice. For any concern about your hearing or a child’s, see an audiologist or doctor.