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Hearing Protection Attenuation Calculator (SNR, HML, NRR)

Estimate the noise reaching the ear under an earplug or earmuff from its SNR, HML or NRR rating, with the real-world allowance HSE and OSHA each apply.

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SettingsSettings for this calculationUS
Market
Imperial · sales tax
Which rating the packaging or data sheet gives.

Protectors sold in the UK and EU carry an SNR and usually H, M and L values as well; the HML method is the better of the two where the noise is dominated by low or high frequencies. US products carry an NRR under EPA labelling rules. Use the rating for the product actually worn, not a family figure.

The measured A-weighted level at the worker's position — used by the HML and A-weighted NRR methods.

The equivalent continuous A-weighted level the protector is being chosen for, measured without the protector. The SNR method does not use it; the HML method uses it with the C-weighted level; and the NRR method uses it when the measurement is A-weighted.

The measured C-weighted level at the same position — used by the SNR, HML and C-weighted NRR methods.

Most sound level meters read C-weighting as well as A. The difference between the two is what tells the HML method how much low-frequency energy there is: a C-weighted level well above the A-weighted one means low-frequency noise, which protectors stop less well.

The single number rating printed on the protector.

Printed on the packaging of any protector sold in the UK and EU, tested to EN ISO 4869-2. Typical figures run from the low twenties for a light earmuff to the mid-thirties for a well-fitted foam earplug.

Whether to reduce the rating for how protectors are actually worn.

Laboratory ratings come from trained subjects fitting the protector perfectly. HSE advises taking 4 dB off any protector's protection for real-world use; the OSHA Technical Manual halves the NRR-based attenuation. Leaving the allowance off gives the best case, not the expected one.

Estimated level at the ear

72 dB(A)

ComparisonA comparison, not a check — no result here is an approval.

At 72.0 dB(A) the estimate is inside the 70 to 80 dB(A) band HSE advises aiming for at the ear. The estimate assumes the protector is worn correctly for the whole time in the noise; only fit testing or an in-ear measurement shows the level actually reaching the ear.

Level the rating is deducted from
98 dB(C)
Protection assumed
26 dB
Real-world allowance taken off the rating
4 dB
Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

  • BS EN ISO 4869-2 and HSE L108: with the SNR, the A-weighted level under the protector is LC − SNR; with the H, M and L values, the predicted noise level reduction is PNR = M − (H − M)(LC − LA − 2) ÷ 4 where LC − LA is 2 dB or less and PNR = M − (M − L)(LC − LA − 2) ÷ 8 where it is more, and the level at the ear is LA − PNR
  • HSE L108 (Controlling noise at work): to allow for real-world factors, reduce the protection of any hearing protector by 4 dB; aim for a level at the ear between 70 and 80 dB(A), since protection taking it below 70 dB(A) over-protects and isolates the wearer
  • 29 CFR 1910.95, Appendix B: where the noise is measured A-weighted, subtract 7 dB from the NRR before deducting it, and where it is measured C-weighted, deduct the NRR directly; the OSHA Technical Manual, Section III, Chapter 5, derates the resulting attenuation by 50 per cent to allow for real-world fit

Inputs used

Rating on the Protector
SNR — single number rating (UK, EU and most of the world)
A-Weighted Noise Level, LAeq (dB(A))
95
C-Weighted Noise Level, LCeq (dB(C))
98
SNR (dB)
30
H Value (dB)
32
M Value (dB)
24
L Value (dB)
17
NRR (dB)
29
How the Noise Was Measured
A-weighted (dBA) — the NRR is reduced by 7 dB first
Allow for Real-World Fit
Yes — HSE's 4 dB, or OSHA's 50% for an NRR

Intermediate steps

Level the rating is deducted from
98 dB(C)
Protection assumed
26 dB
Real-world allowance taken off the rating
4 dB
Final result72 dB(A)

Confidence note: At 72.0 dB(A) the estimate is inside the 70 to 80 dB(A) band HSE advises aiming for at the ear. The estimate assumes the protector is worn correctly for the whole time in the noise; only fit testing or an in-ear measurement shows the level actually reaching the ear.

What this calculation does not cover

  • The ratings come from laboratory tests with a perfect fit. Long hair, spectacle arms, a hood, a badly inserted earplug and a protector removed for part of the time all cut the protection achieved — a few minutes without protection in a loud area loses much of its value over the day.
  • The octave-band method in BS EN ISO 4869-2 is more accurate than either SNR or HML where the spectrum is known, and is not implemented here.
  • It estimates the steady level at the ear. Impulse noise, where the peak matters, needs the protector checked against the peak values as well.
  • Plugs and muffs worn together do not add their ratings; the combination gains far less than the sum, and no simple rating predicts it.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-21 · v1.0.0

Regulatory standards & verification citations3
  1. BS EN ISO 4869-2 and HSE L108: with the SNR, the A-weighted level under the protector is LC − SNR; with the H, M and L values, the predicted noise level reduction is PNR = M − (H − M)(LC − LA − 2) ÷ 4 where LC − LA is 2 dB or less and PNR = M − (M − L)(LC − LA − 2) ÷ 8 where it is more, and the level at the ear is LA − PNR
  2. HSE L108 (Controlling noise at work): to allow for real-world factors, reduce the protection of any hearing protector by 4 dB; aim for a level at the ear between 70 and 80 dB(A), since protection taking it below 70 dB(A) over-protects and isolates the wearer
  3. 29 CFR 1910.95, Appendix B: where the noise is measured A-weighted, subtract 7 dB from the NRR before deducting it, and where it is measured C-weighted, deduct the NRR directly; the OSHA Technical Manual, Section III, Chapter 5, derates the resulting attenuation by 50 per cent to allow for real-world fit

Which documents these citations point at

Standards referenced: ISO 4869-2 (International Organization for Standardization, International).

Cite this page

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How to calculate hearing protection attenuation (SNR, HML, NRR) in 11 steps

  1. Rating on the ProtectorWhich rating the packaging or data sheet gives.
  2. A-Weighted Noise Level, LAeq (dB(A))The measured A-weighted level at the worker's position — used by the HML and A-weighted NRR methods.
  3. C-Weighted Noise Level, LCeq (dB(C))The measured C-weighted level at the same position — used by the SNR, HML and C-weighted NRR methods.
  4. SNR (dB)The single number rating printed on the protector.
  5. H Value (dB)The protector's rating for high-frequency noise.
  6. M Value (dB)The protector's rating for mid-frequency noise.
  7. L Value (dB)The protector's rating for low-frequency noise.
  8. NRR (dB)The noise reduction rating on the US packaging.
  9. How the Noise Was MeasuredWhether the level the NRR is deducted from is A- or C-weighted.
  10. Allow for Real-World FitWhether to reduce the rating for how protectors are actually worn.
  11. Estimated level at the earThe tool computes the estimated level at the ear from those figures and shows the formula, its sources, and a confidence rating alongside it.

Frequently asked questions

Why does a protector rated 30 dB not take 30 dB off?
Because the rating is measured in a laboratory, on people trained to fit it perfectly, and real use is not like that. Earplugs are seldom inserted as deeply, muffs sit over spectacle arms and hair, and protectors come off for a moment in the middle of noisy work. HSE advises taking 4 dB off any rating for real-world use; for US NRRs, OSHA's guidance halves the protection. Even then the figure is an estimate, and fit training does more for the real number than a higher rating does.
Should I use the SNR or the HML method?
The HML method where you have both the A- and C-weighted levels, because it accounts for what kind of noise it is. Low-frequency noise — big engines, compressors, vibrating plant — is harder to stop, and a protector's L value is always its lowest; the SNR averages that away. The octave-band method is better still where a full spectrum has been measured, and it is what a specialist would use for a difficult case.
How is an NRR used on a US site?
If the noise was measured with A-weighting, as most dosimeters and meters report it, OSHA's Appendix B subtracts 7 dB from the NRR and deducts the rest; with a C-weighted measurement the NRR is deducted as printed. The OSHA Technical Manual then halves the protection to allow for real-world fit, so an NRR of 29 against 100 dBA leaves about 89 dBA at the ear rather than the 78 the printed figure suggests.
Is more protection always better?
No. HSE advises aiming for 70 to 80 dB(A) at the ear and treats less than 70 as over-protection: a worker who cannot hear warnings, reversing alarms or speech is more likely to lift the protector off, which costs far more protection than the extra rating bought. The best protector is the one that brings the level into that band and is comfortable enough to be worn for the whole time in the noise.
Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.