Time-weighted Average (TWA) Noise Exposure Calculator

Calculator determines partial and total 8-hour time-weighted average exposures and noise doses.


Employee works for 2.5 hours in 90 dBA and 5.5 hours in 85 dBA.
Enter 90 dBA, 2 hours and 30 minutes for location 1 and 85 dBA, 5 hours, and 30 minutes for location 2.
The result for this would be a TWA of 87 dBA and a dose of 65.7%.

Key Fact: OSHA's maximum allowable daily 8-hour TWA with protection is 90 dBA or 100% noise dose.

Calculate 8-hour Time-Weighted Average (TWA) and Noise Dose
Location Noise Exposure Duration TWA Dose Level
1 dBA : H:m
2 dBA : H:m
3 dBA : H:m
4 dBA : H:m
5 dBA : H:m

OSHA Requirements for Calculated TWA

  • No OSHA requirements per 29 CFR 1910.95
  • Notify worker that his/her noise exposure meets or exceeds 85 dBA 8-hour TWA
  • Allow worker to observe noise measurements
  • Implement engineering and administrative controls to reduce exposure if possible
  • Provide hearing protectors to worker at no cost
  • Ensure worker wears hearing protectors
  • Ensure worker wears hearing protectors if he does not have a baseline or experiences an STS
  • Place worker in audiometric testing program
  • Conduct baseline audiogram within 6 months of worker's first exposure at or above 85 dBA
  • Conduct annual audiograms thereafter
  • Train worker in effects of noise, purpose and use of hearing protectors, and purpose of audiometric testing
  • Repeat noise monitoring if change to production, process, equipment or controls


  • Use personal earplug attenuation testing to verify that worn protectors meet OSHA requirements. See our E-A-RFit service

Key Definitions

  • 8-Hour Time-Weighted Average: Average noise exposure figured for an 8-hour period.
  • Permissible Exposure Level (PEL): Maximum allowable 8-hour TWA noise exposure (OSHA's limit is 90 dBA).
  • Noise Dose: Percent of PEL to which worker exposed. 90 dBA 8-hour TWA equals a dose of 100%. An 85 dBA 8-hour TWA equals 50%. The exchange rate is used to figure this.
  • Exchange Rate: Amount of dBA at which noise dose doubles. OSHA uses a 5 dBA exchange rate which means that a worker exposed to 95 dBA receives twice the dose of 90 dBA.
  • Noise dosimeters: Devices used in sound surveys to calculate noise exposure.

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