What is NRR and SNR derating?
Laboratory attenuation ratings (NRR in the US, SNR in much of Europe) overstate real-world protection. Derating methods reduce the labelled value so field estimates are more realistic.
Enter the workplace level and the protector’s NRR or SNR below, choose OSHA, NIOSH, or SNR derating, and see the estimated protected level. Pair this tool with the noise exposure calculator when you need daily dose or TWA from multiple tasks.
Hearing Protection Calculator
Hearing protection · NRR / SNR derating
Estimate protected noise level with OSHA, NIOSH, or simplified SNR derating. Single protection only — not dual plugs + muffs.
Formula: OSHA: L − (NRR − 7) ÷ 2 · NIOSH: L − (NRR × derate) · SNR: L − (SNR − 4)
- Use NRR with OSHA/NIOSH methods and SNR with the SNR method — do not mix labels.
- Single protection only; dual protection needs a different adjustment.
- Pair with the noise dose calculator for multi-task daily exposure.
Methods in this calculator
- OSHA (single protection): Protected ≈ L − (NRR − 7) ÷ 2
- NIOSH: Protected ≈ L − (NRR × derate) with derate 0.75 muffs / 0.50 formable plugs / 0.30 other plugs
- SNR (simplified): Protected ≈ L − (SNR − 4) — a common field approximation for assumed protection
Worked examples
- 95 dB(A), NRR 30, OSHA → attenuation (30−7)÷2 = 11.5 → protected ≈ 83.5 dB(A)
- 95 dB(A), NRR 30, NIOSH muffs (×0.75) → 22.5 dB → protected ≈ 72.5 dB(A)
- 95 dB(A), SNR 34 → 34−4 = 30 dB → protected ≈ 65 dB(A)
How to read the result
- Compare the protected level with your target (often ≤ 85 dB(A) for many hearing-conservation programmes — confirm locally).
- If protected level stays high, improve fit, change protector class, add engineering controls, or reduce time exposed.
- Dual protection (plugs + muffs) needs a different rule — this tool is for single protection only.
Fit and real-world use
- Derating cannot fix a poor fit — training and fit-testing matter more than the label.
- Remove protectors for short “just a minute” tasks and you lose the daily benefit.
- Replace worn plugs and cushions; dirty or damaged gear under-protects.
Frequently asked questions
Which method should I use?
Follow your jurisdiction and company hearing-conservation procedure. OSHA derating is common in US compliance discussions; NIOSH is more conservative for many field estimates; SNR suits labelled European protectors.
Is the protected level a compliance guarantee?
No. It is an estimate from derating formulas. Dosimetry, octave-band methods, and fit-testing give stronger evidence for programmes.
Can I use this for dual protection?
Not with these single-protection formulas. OSHA and other bodies publish separate dual-protection adjustments — use those when wearing plugs and muffs together.
NRR vs SNR — can I convert them?
They come from different test standards. Do not treat NRR and SNR as interchangeable. Use the rating printed on your protector with the matching method.
