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Noise dose and TWA calculator

Enter the sound levels and hours of a work day to get the noise dose and 8-hour TWA the way 29 CFR 1910.95 Appendix A computes them, with the exact words of the rule.

Fact-checked against official sources (eCFR text as of Nov 3, 2026) · Last checked

Enter each period of the work day: its A-weighted sound level (slow response) and how long it lasted. Your input

Period 1
Period 2

Levels are whole decibels from 80 to 130, the rows of Table G-16a. Sound below 80 dBA is left out because the rule integrates 80 to 130 decibels.

“All continuous, intermittent and impulsive sound levels from 80 decibels to 130 decibels shall be integrated into the noise measurements.”
29 CFR 1910.95(d)(2)(i)

Noise dose and 8-hour TWA Our calculation

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TWA —

Add at least one period to see the dose.

“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. For purposes of the hearing conservation program, employee noise exposures shall be computed in accordance with appendix A and Table G-16a, and without regard to any attenuation provided by the use of personal protective equipment.”
29 CFR 1910.95(c)(1)

How it is worked out

“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.”
29 CFR 1910.95, Appendix A (mandatory), I(1)(ii)
“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.”
29 CFR 1910.95, Appendix A (mandatory), I(2)

This is the hearing conservation program calculation. The permissible exposure limits are in Table G-16, and exposures above them call for controls:

“When employees are subjected to sound exceeding those listed in Table G-16, feasible administrative or engineering controls shall be utilized. If such controls fail to reduce sound levels within the levels of Table G-16, personal protective equipment shall be provided and used to reduce sound levels within the levels of the table.”
29 CFR 1910.95(b)(1)

A study aid. Real exposures are measured with a sound level meter or dosimeter, and hearing protection is not subtracted.

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