Estimate a level under one hearing protector using the OSHA NRR method appropriate to the measurement weighting and calculation purpose.
OSHA NRR Formulas
For an A-weighted measurement, OSHA Appendix B estimates the A-weighted level under the protector by subtracting NRR − 7. For a C-weighted measurement, it subtracts the labeled NRR directly. These are estimates and depend on correct, consistent wear.
OSHA sometimes applies a 50% safety factor to laboratory attenuation when evaluating the benefit of engineering controls. OSHA states that this extra factor is not used to evaluate hearing-protector adequacy under the hearing conservation program. The calculator therefore keeps those contexts separate.
NIOSH 2025 Fit-Testing Update
NIOSH’s 2025 policy update supersedes its 1998 generic, device-specific NRR derating guidance and recommends individual quantitative fit testing. This page does not reproduce the obsolete 25%, 50%, or 70% device derating factors. A personal attenuation rating is more informative than a package NRR for an individual worker.
The result does not account for intermittent wear, poor seal, eyewear, other protective equipment, dual protection, impulsive noise, or measurement uncertainty. Engineering and administrative controls remain primary; a hearing-conservation professional should assess protector selection and fit.
Primary references: OSHA 1910.95 Appendix B, OSHA interpretation of NRR safety factors, and NIOSH 2025 Individual Fit-Testing Recommendation.
