What is the difference between OSHA and NIOSH noise standards?

OSHA (29 CFR 1910.95) sets the permissible 8-hour exposure limit at 90 dBA with a 5 dB exchange rate (doubling dose every 5 dB). NIOSH recommends a stricter 85 dBA criterion with a 3 dB exchange rate (doubling every 3 dB), which is closer to most international standards.

What does noise dose percentage mean?

A dose of 100% means you have reached the full permissible daily exposure. A dose above 100% means the limit has been exceeded. OSHA requires hearing conservation programs at 50% dose (action level) and engineering/administrative controls or hearing protection when dose exceeds 100%.

What is TWA (time-weighted average)?

TWA is the equivalent constant noise level over an 8-hour workday that would produce the same dose as the actual varying exposures. It is the standard metric reported to regulators.

Why can I enter a noise level as low as 70 dBA?

Exposures below 80 dBA generally contribute negligible dose under both standards, but this calculator still includes them for completeness. OSHA only counts levels at or above 90 dBA toward the dose; however, this tool computes NIOSH dose for all entered levels as NIOSH includes contributions from 80 dBA upward.

Noise Exposure Calculator

Name: Noise Exposure Calculator
Availability: InStock
Author: Nham Vu

Calculate occupational noise dose and permissible exposure time per OSHA and NIOSH standards.

Standard: Both OSHA & NIOSH OSHA only NIOSH only

Noise Sources

#	Source / Description	Level (dBA)	Hours/Day

Per-Source Breakdown

Source	dBA	Hours	OSHA Ti (h)	NIOSH Ti (h)	OSHA Ci/Ti	NIOSH Ci/Ti

Source	Typical dBA	OSHA Ti (h)	NIOSH Ti (h)

Summary

Calculate occupational noise dose and permissible exposure time per OSHA and NIOSH standards.

How it works

Enter the dBA level and daily exposure hours for each noise source (up to 5 sources).
The calculator applies the OSHA formula Ti = 8 / 2^((L-90)/5) and the NIOSH formula Ti = 8 / 2^((L-85)/3) to find the permissible hours at each level.
Noise dose percentage is computed as D% = sum(Ci/Ti) × 100, where Ci is actual exposure time.
Time-weighted average (TWA) is derived from the dose: TWA = 16.61 × log10(D/100) + criterion level.
Results above 100% dose indicate the daily permissible limit is exceeded, requiring hearing protection or engineering controls.

Use cases

Safety officers verifying worker noise exposure on a factory floor.
Industrial hygienists calculating TWA for OSHA compliance documentation.
Engineers assessing whether additional noise controls are needed for a job site.
Health and safety students learning the OSHA vs NIOSH exchange rate difference.

Frequently Asked Questions

Last updated: 2026-07-24 · Reviewed by Nham Vu