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Calcimator

Sound Masking Calculator

Calculate OSHA noise dose and time-weighted average (TWA) from multiple exposure periods. Determines compliance with OSHA PEL (90 dBA / 8 hr) using the 5 dB exchange rate.

About this calculator

This calculator computes OSHA occupational noise dose across up to four exposure periods, using the permissible exposure time formula from 29 CFR 1910.95 (Ti = 8 / 2^((Li-90)/5)) with OSHA's 5 dB exchange rate and 90 dBA / 8-hour criterion. Each period's dose contribution is its duration divided by the allowable time at that level, summed across all active periods (periods with zero duration contribute nothing) and reported as Noise Dose in percent, where 100% is the permissible exposure limit. Because the exchange rate is 5 dB rather than a linear scale, dose grows exponentially with level, not proportionally -- each 5 dB increase in a period's level doubles that period's contribution to dose.

Period 1 Level is the dominant input at this calculator's default settings, since Period 1 defaults to a full 8-hour duration while Periods 2-4 default to zero duration and contribute nothing until a duration is entered for them. TWA (Time-Weighted Average) converts the dose percentage back into an equivalent steady 8-hour sound level using OSHA's TWA = 16.61 x log10(D/100) + 90 formula, so a TWA reading of exactly 90 dBA corresponds to exactly 100% dose. OSHA sets two thresholds on Noise Dose: 50% triggers the hearing-conservation action level, and 100% is the enforceable permissible exposure limit requiring engineering or administrative controls.

Inputs

Results

Noise dose (%)

100

TWA (dBA)90
Max allowable exposure (hrs)8
Remaining time at 90 dBA (hrs)0
Compliance (0/1/2)1
Total exposure (hrs)8

Figures current as of 1981. Source: 29 CFR 1910.95, Occupational Noise Exposure (Hearing Conservation Amendment, 46 FR 4161, Jan. 16, 1981), Table G-16a and Appendix A

How to Use This Calculator
  1. Enter Period 1 level (dBA), Period 1 duration (hrs), and Period 2 level (dBA).
  2. Set Period 2 duration (hrs), Period 3 level (dBA), and Period 3 duration (hrs).
  3. Adjust Period 4 level (dBA), Period 4 duration (hrs) as needed.
  4. Review the Noise dose (%) result.
  5. Use TWA (dBA) and Max allowable exposure (hrs) to inform your decision.

How the result changes with Period 1 level (dBA)

Period 1 level (dBA)Noise dose (%)
8025
13551,200
140102,400

What each input means

Period 1 level (dBA)
Sound level in dBA for the first exposure period.
Period 1 duration (hrs)
Duration of the first exposure period in hours.
Period 2 level (dBA)
Sound level for the second exposure period (set duration to 0 to skip).
Period 2 duration (hrs)
Duration of the second exposure period in hours.
Period 3 level (dBA)
Sound level for the third exposure period.
Period 3 duration (hrs)
Duration of the third exposure period in hours.
Period 4 level (dBA)
Sound level for the fourth exposure period.
Period 4 duration (hrs)
Duration of the fourth exposure period in hours.

What each result means

Noise dose (%)
OSHA noise dose percentage. 100% = permissible exposure limit. >50% triggers action level.
TWA (dBA)
8-hour Time-Weighted Average noise level. OSHA PEL = 90 dBA, action level = 85 dBA.
Max allowable exposure (hrs)
Maximum hours at this dose rate before reaching 100% dose.
Remaining time at 90 dBA (hrs)
Hours remaining at 90 dBA before reaching 100% dose.
Compliance (0/1/2)
0 = Below action level, 1 = Action level (hearing conservation needed), 2 = Exceeds PEL.
Total exposure (hrs)
Sum of all exposure period durations.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Period 1 level (dBA) = 90, Period 1 duration (hrs) = 8, Period 2 level (dBA) = 95, Period 2 duration (hrs) = 0 = 8 input(s) provided
  2. Calculate Noise dose
    Noise dose = totalDoseFraction * 100
    100 = 100
  3. Calculate TWA
    TWA
    90 = 90
  4. Calculate Max allowable exposure
    8 = 8

Figures and sources

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

What input matters most for the noise dose result?

Period 1 Level, at this calculator's default settings -- Period 1 defaults to a full 8-hour duration, while Periods 2 through 4 default to zero duration and contribute nothing to Noise Dose until you give them a nonzero duration. Once a period has a nonzero duration, its level matters just as much as Period 1's does.

Why does a small increase in sound level raise the dose so much?

Because OSHA's permissible exposure formula uses a 5 dB exchange rate: each 5 dB increase in level halves the allowable exposure time, which doubles that period's contribution to Noise Dose for the same duration. That exponential relationship is why noise dose can climb steeply even from what sounds like a modest increase in level.

What is the relationship between TWA and noise dose?

TWA converts the dose percentage into an equivalent constant 8-hour sound level using TWA = 16.61 x log10(Dose/100) + 90. A Noise Dose of exactly 100% produces a TWA of exactly 90 dBA (the OSHA permissible exposure limit); dose above or below 100% produces a TWA above or below 90 dBA respectively.

What's the difference between the 50% and 100% dose thresholds?

50% dose (TWA 85 dBA) is OSHA's hearing-conservation action level, which triggers audiometric testing and a hearing conservation program but does not by itself require engineering controls. 100% dose (TWA 90 dBA) is the permissible exposure limit -- exceeding it requires engineering or administrative controls, or hearing protection where those aren't feasible.

Does entering a level for an unused period change the result?

The level field for Period 2, 3, or 4 only appears once you set that period's duration above zero -- the calculator filters out any period with zero duration before summing dose contributions, so there's no level to enter until you give that period a nonzero duration to represent actual exposure time at that level.

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