NIOSH · OSHA · WHO
Noise exposure calculator
How long a day can you spend at a given noise level, and how much of the daily limit did your shift use? Type levels in A-weighted decibels (dBA).
Allowed time at one level
One steady level, for as long as you are exposed to it.
a day. 8 h at 85 dBA, halved for every 3 dB more.
a day. Hearing conservation program from 2 h 18 min.
a week of listening. Children and sensitive listeners: 30 min a week.
Daily noise dose
One row per noise: its level and how long you spent in it today.
8-hour TWA 89.2 dBA. Over the recommended limit by 166 % of dose.
8-hour TWA 84.3 dBA. Well under the permissible limit.
8-hour TWA 87.1 dBA. At or over the action level: OSHA requires a hearing conservation program.
| Exposure | Level · time | NIOSH allows | NIOSH dose | OSHA allows | OSHA PEL / action |
|---|---|---|---|---|---|
| Angle grinder | 100.0 dBA · 15 min | 15 min | 100 % | 2 h | 13 % / 13 % |
| Workshop machines | 92.0 dBA · 2 h | 1 h 35 min | 126 % | 6 h 4 min | 33 % / 33 % |
| Assembly area | 84.0 dBA · 4 h | 10 h 5 min | 40 % | not counted | – / 22 % |
| Break room | 65.0 dBA · 1 h | not counted | – | not counted | – / – |
| Total | 7 h 15 min | 266 % | 45 % / 67 % |
How the limits work
Both US limits allow 8 hours at a reference level and shorten the time as the level rises. NIOSH, the research agency, recommends 85 dBA for 8 hours and halves the time for every 3 dB more, because 3 dB is a doubling of sound energy: 4 hours at 88 dBA, 1 hour at 94, 15 minutes at 100. OSHA, the regulator, allows 90 dBA for 8 hours and halves the time every 5 dB, so it permits 4 hours at 95 dBA where NIOSH recommends 30 minutes at 97.
The dose adds up each exposure as a share of its allowed time: 2 hours where 4 are allowed is 50 %. A dose of 100 % is the limit, and the TWA is the steady 8-hour level that would give the same dose. OSHA also has an action level: at a TWA of 85 dBA (a 50 % dose, counting levels from 80 dBA) employers must run a hearing conservation program with hearing tests and protectors. For the PEL itself OSHA counts only levels of 90 dBA and above, and NIOSH counts from 80 dBA.
The WHO tile is for listening rather than work: WHO and ITU set 80 dB for 40 hours a week for adults and 75 dB for children, halving every 3 dB.
Levels should be A-weighted averages over each period, ideally from a dosimeter or a calibrated meter. Readings from a phone are rough estimates. These limits protect most people, not everyone, and this page is not medical or legal advice.
Questions
Why do NIOSH and OSHA give different times?
OSHA's limit dates from 1971 and uses 90 dBA with a 5 dB exchange rate, which assumes the ears recover during quieter breaks. NIOSH reviewed the evidence in 1998 and recommends 85 dBA with a 3 dB exchange rate, which follows the equal-energy rule and protects more workers. The OSHA limit is the legal one for most US employers; the NIOSH one is the safer target.
Do earplugs change the dose?
The dose here is the noise around you, which is how both standards measure exposure. Hearing protection lowers what reaches your ears; the sound level chart page estimates by how much from a protector's NRR, using the OSHA and NIOSH derating rules.
What if my shift is longer than 8 hours?
Enter every period, however long the day. The dose counts all of it, so 10 hours at 85 dBA comes to 125 % under NIOSH even though each hour is at the reference level. The TWA is still expressed as an 8-hour equivalent.
Sources
- NIOSH, Criteria for a Recommended Standard: Occupational Noise Exposure, Revised Criteria 1998, DHHS (NIOSH) Publication No. 98-126: 85 dBA REL, 3 dB exchange rate, 80 to 140 dBA integrated, 140 dBA ceiling, TWA = 10.0 × log(D/100) + 85.
- OSHA, 29 CFR 1910.95 Occupational noise exposure, Table G-16 and the action level in paragraph (c), and Appendix A, Noise exposure computation: T = 8 / 2^((L − 90)/5), D = 100 C/T, TWA = 16.61 log10(D/100) + 90.
- OSHA Technical Manual, Section III, Chapter 5: Noise (90 dBA threshold for the PEL, 80 dBA for the action level).
- WHO and ITU, Safe listening devices and systems: a WHO-ITU standard (2019), and WHO, Safe listening questions and answers.