Noise dose and TWA calculator
Add each period of a work shift at a given A-weighted sound level. The calculator applies OSHA's Appendix A method with Table G-16a reference durations.
| Sound level (dBA) | Hours (C) | T (hours) | C/T | |
|---|---|---|---|---|
| 6.1 | 0.656 | |||
| 4 | 0.500 | |||
| 16 | 0.125 |
Formulas and sources
D = 100 × (C1/T1 + C2/T2 + … + Cn/Tn) · TWA = 16.61 log10(D/100) + 90 · T = 8 ÷ 2^((L − 90)/5)
For whole-decibel levels from 80 to 130 dBA, T comes straight from Table G-16a. For other levels it uses the exponential formula above, which is the same 5-dB exchange rate that generates the table. That formula is shown as an image in the eCFR footnote to Table G-16a.
“When the workshift noise exposure is composed of two or more periods of noise at different levels, the total noise dose over the work day is given by: D = 100(C1 / T1 + C2 / T2 + Cn / Tn), where Cn indicates the total time of exposure at a specific noise level, and Tn indicates the reference duration for that level as given by Table G-16a.”
“The eight-hour time-weighted average sound level (TWA), in decibels, may be computed from the dose, in percent, by means of the formula: TWA = 16.61 log10 (D/100) + 90.”
“The employer shall administer a continuing, effective hearing conservation program, as described in paragraphs (c) through (o) of this section, whenever employee noise exposures equal or exceed an 8-hour time-weighted average sound level (TWA) of 85 decibels measured on the A scale (slow response) or, equivalently, a dose of fifty percent.”
FAQ
How does OSHA calculate noise dose?
Under 29 CFR 1910.95 Appendix A, D = 100 × (C1/T1 + C2/T2 + … + Cn/Tn), where C is the time spent at each sound level and T is the reference duration for that level from Table G-16a.
How do I convert dose to an 8-hour TWA?
TWA = 16.61 × log10(D/100) + 90. A 100% dose equals a TWA of 90 dBA, and a 50% dose equals 85 dBA.
What dose triggers a hearing conservation program?
A TWA of 85 dBA or, equivalently, a 50% dose: OSHA's action level in 1910.95(c).
For hearing conservation purposes, 1910.95(d)(2)(i) integrates sound levels from 80 to 130 dBA. Levels below 80 dBA are ignored here. Compliance with the permissible exposure limit in 1910.95(b) uses Table G-16. This tool is for study and estimation, not a substitute for a qualified noise survey.
Noise calculations are in ASP11 Domain 1. Practice with cited calculation questions and hearing conservation questions.