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OSHA Noise Dose and 8-Hour TWA Calculator

OSHA's noise dose and 8-hour TWA from periods at measured levels, on both the hearing-conservation and PEL bases, with the NIOSH figure beside them.

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The A-weighted, slow-response sound level during this part of the shift.

The level a sound level meter set to A-weighting and slow response reads over this period, or a dosimeter's logged level for it. Periods at similar levels can share one row, and a row with no time against it is ignored.

Hours spent at this level — minutes divided by 60.

The time actually spent at the period's level. Fifteen minutes is 0.25 hours. Time below 80 dBA can be left out: OSHA's measurement does not count it towards either dose.

The A-weighted, slow-response sound level during this part of the shift.

The level a sound level meter set to A-weighting and slow response reads over this period, or a dosimeter's logged level for it. Periods at similar levels can share one row, and a row with no time against it is ignored.

Hours spent at this level — minutes divided by 60.

The time actually spent at the period's level. Fifteen minutes is 0.25 hours. Time below 80 dBA can be left out: OSHA's measurement does not count it towards either dose.

The A-weighted, slow-response sound level during this part of the shift.

The level a sound level meter set to A-weighting and slow response reads over this period, or a dosimeter's logged level for it. Periods at similar levels can share one row, and a row with no time against it is ignored.

Hours spent at this level — minutes divided by 60.

The time actually spent at the period's level. Fifteen minutes is 0.25 hours. Time below 80 dBA can be left out: OSHA's measurement does not count it towards either dose.

The A-weighted, slow-response sound level during this part of the shift.

The level a sound level meter set to A-weighting and slow response reads over this period, or a dosimeter's logged level for it. Periods at similar levels can share one row, and a row with no time against it is ignored.

Hours spent at this level — minutes divided by 60.

The time actually spent at the period's level. Fifteen minutes is 0.25 hours. Time below 80 dBA can be left out: OSHA's measurement does not count it towards either dose.

8-hour TWA — hearing-conservation basis (80 dBA threshold, 5 dB exchange)

88.1 dBA

ComparisonA comparison, not a check — no result here is an approval.

The hearing-conservation dose is 77%: the action level in 29 CFR 1910.95(c) is 50%, an 8-hour TWA of 85 dBA. The permissible-exposure dose, counting only sound from 90 dBA, is 33%: the PEL is 100%, an 8-hour TWA of 90 dBA. NIOSH's recommended limit, which is advisory, puts the same day at 234%. A dose under the action level is not a finding that the exposure is safe; NIOSH's recommended limit is set lower for that reason.

Noise dose — hearing-conservation basis (sound from 80 dBA)
77.13 %
Noise dose — permissible-exposure basis (sound from 90 dBA)
32.99 %
8-hour TWA — permissible-exposure basis
82 dBA
NIOSH dose (85 dBA, 3 dB exchange)
233.87 %
NIOSH 8-hour TWA
88.69 dBA
Period 1: time OSHA's table permits at 92.0 dBA
6.06 hours
Period 2: time OSHA's table permits at 88.0 dBA
10.56 hours
Period 3: time OSHA's table permits at 80.0 dBA
32 hours
Then change the inputs to see how far the answer moves.

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How this was calculated

Formula source(s)

  • 29 CFR 1910.95, Appendix A: the reference duration at a level L is T = 8 ÷ 2^((L − 90) ÷ 5) hours; the dose is D = 100 × (C1/T1 + C2/T2 + … + Cn/Tn) per cent, where Cn is the time spent at each level; and the 8-hour time-weighted average is TWA = 16.61 × log10(D ÷ 100) + 90
  • 29 CFR 1910.95(b)(1), Table G-16, and 29 CFR 1926.52, Table D-2 for construction: a permissible exposure limit of 90 dBA for 8 hours with a 5 dB exchange rate; 29 CFR 1910.95(c)(1): an action level for a hearing conservation program of an 8-hour TWA of 85 dBA, a dose of 50 per cent
  • 29 CFR 1910.95(d)(2)(i) and the OSHA Technical Manual, Section III, Chapter 5: all sound from 80 dBA to 130 dBA is integrated for the hearing-conservation measurement, while the permissible-exposure dose counts only sound at or above 90 dBA — the 80 and 90 dBA thresholds dosimeters are set to for each
  • NIOSH, Criteria for a Recommended Standard: Occupational Noise Exposure (Publication 98-126): a recommended exposure limit of 85 dBA as an 8-hour TWA with a 3 dB exchange rate, T = 8 ÷ 2^((L − 85) ÷ 3) hours

Inputs used

Period 1 Sound Level (dBA)
92
Period 1 Duration (hours)
2
Period 2 Sound Level (dBA)
88
Period 2 Duration (hours)
4
Period 3 Sound Level (dBA)
80
Period 3 Duration (hours)
2
Period 4 Sound Level (dBA)
70
Period 4 Duration (hours)
0

Intermediate steps

Noise dose — hearing-conservation basis (sound from 80 dBA)
77.13 %
Noise dose — permissible-exposure basis (sound from 90 dBA)
32.99 %
8-hour TWA — permissible-exposure basis
82 dBA
NIOSH dose (85 dBA, 3 dB exchange)
233.87 %
NIOSH 8-hour TWA
88.69 dBA
Period 1: time OSHA's table permits at 92.0 dBA
6.06 hours
Period 2: time OSHA's table permits at 88.0 dBA
10.56 hours
Period 3: time OSHA's table permits at 80.0 dBA
32 hours
Final result88.13 dBA

Confidence note: The hearing-conservation dose is 77%: the action level in 29 CFR 1910.95(c) is 50%, an 8-hour TWA of 85 dBA. The permissible-exposure dose, counting only sound from 90 dBA, is 33%: the PEL is 100%, an 8-hour TWA of 90 dBA. NIOSH's recommended limit, which is advisory, puts the same day at 234%. A dose under the action level is not a finding that the exposure is safe; NIOSH's recommended limit is set lower for that reason.

What this calculation does not cover

  • It works from the levels and durations you enter. A dosimeter worn for the whole shift integrates the real variation and is the measurement OSHA's rule describes; a task-by-task estimate is a planning figure.
  • Impulse noise has its own ceiling: 29 CFR 1910.95 says exposure to impulsive or impact noise should not exceed 140 dB peak, which no TWA shows.
  • Table G-16 permits no exposure above 115 dBA, and 130 dBA is the top of the integration range. The formula still returns a dose for such levels, and that dose does not describe a permitted exposure.
  • Hearing protection is not deducted; the level under a protector is the hearing-protection page's question.
  • States running their own OSHA-approved plans can set rules stricter than the federal standard, and the construction standard, 29 CFR 1926.52, carries the same exposure table without the general-industry action-level provisions.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-21 · v1.0.0

Regulatory standards & verification citations4
  1. 29 CFR 1910.95, Appendix A: the reference duration at a level L is T = 8 ÷ 2^((L − 90) ÷ 5) hours; the dose is D = 100 × (C1/T1 + C2/T2 + … + Cn/Tn) per cent, where Cn is the time spent at each level; and the 8-hour time-weighted average is TWA = 16.61 × log10(D ÷ 100) + 90
  2. 29 CFR 1910.95(b)(1), Table G-16, and 29 CFR 1926.52, Table D-2 for construction: a permissible exposure limit of 90 dBA for 8 hours with a 5 dB exchange rate; 29 CFR 1910.95(c)(1): an action level for a hearing conservation program of an 8-hour TWA of 85 dBA, a dose of 50 per cent
  3. 29 CFR 1910.95(d)(2)(i) and the OSHA Technical Manual, Section III, Chapter 5: all sound from 80 dBA to 130 dBA is integrated for the hearing-conservation measurement, while the permissible-exposure dose counts only sound at or above 90 dBA — the 80 and 90 dBA thresholds dosimeters are set to for each
  4. NIOSH, Criteria for a Recommended Standard: Occupational Noise Exposure (Publication 98-126): a recommended exposure limit of 85 dBA as an 8-hour TWA with a 3 dB exchange rate, T = 8 ÷ 2^((L − 85) ÷ 3) hours
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How to calculate OSHA noise dose and 8-Hour TWA in 9 steps

  1. Period 1 Sound Level (dBA)The A-weighted, slow-response sound level during this part of the shift.
  2. Period 1 Duration (hours)Hours spent at this level — minutes divided by 60.
  3. Period 2 Sound Level (dBA)The A-weighted, slow-response sound level during this part of the shift.
  4. Period 2 Duration (hours)Hours spent at this level — minutes divided by 60.
  5. Period 3 Sound Level (dBA)The A-weighted, slow-response sound level during this part of the shift.
  6. Period 3 Duration (hours)Hours spent at this level — minutes divided by 60.
  7. Period 4 Sound Level (dBA)The A-weighted, slow-response sound level during this part of the shift.
  8. Period 4 Duration (hours)Hours spent at this level — minutes divided by 60.
  9. 8-hour TWA — hearing-conservation basis (80 dBA threshold, 5 dB exchange)The tool computes the 8-hour TWA — hearing-conservation basis (80 dBA threshold, 5 dB exchange) from those figures and shows the formula, its sources, and a confidence rating alongside it.

Frequently asked questions

What is the difference between noise dose and TWA?
They are the same exposure in two forms. The dose is the share of the permitted exposure used up, as a percentage — 100% is the limit. The TWA turns that dose back into the steady level that would deliver it over 8 hours: a 100% dose is a TWA of 90 dBA, a 50% dose is 85 dBA, and a 200% dose is 95 dBA, because under OSHA every 5 dB doubles the dose.
Why does the page show two different OSHA doses?
Because OSHA measures two things with two thresholds. For the hearing conservation program, all sound from 80 dBA up is integrated, and the result is compared with the 85 dBA action level. For the permissible exposure limit, only sound at 90 dBA and above counts. A day spent entirely between 80 and 90 dBA can therefore reach the action level while its permissible-exposure dose is zero.
Why does NIOSH give a higher number for the same day?
NIOSH's recommended limit is 85 dBA rather than 90, and it uses a 3 dB exchange rate — each 3 dB halves the permitted time — where OSHA uses 5. The 3 dB rule follows the physics of sound energy and is the one most other countries use; the 5 dB rule is more permissive at high levels. For the default day here that is the difference between an OSHA dose well under 100% and a NIOSH dose over 200%.
Does this apply on a construction site?
The construction standard, 29 CFR 1926.52, uses the same 90 dBA table and the same way of combining periods, and requires a continuing, effective hearing conservation program where exposures exceed it. The 85 dBA action level and the detailed program requirements are written in the general-industry standard, 29 CFR 1910.95; many construction employers apply them as good practice, and some state plans require more.
Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.