Noise Exposure Calculator

Workplace noise rules don’t just look at how loud something is — they look at how loud it is and for how long. A short burst of loud noise and a long stretch of moderate noise can add up to the same hearing-damage risk. To capture that, regulators combine each exposure into a single daily noise dose and an equivalent 8-hour Time-Weighted Average (TWA): the steady level that, over a full 8-hour shift, would deliver the same total “dose” as your varying day.

For each row you enter, the tool works out the allowed time T at that level (how many hours you could spend there before reaching the daily limit), then divides your actual time C by it. Add up every C/T and multiply by 100 to get the dose percentage. 100 % dose is the limit; above that you are over the standard for the day. If you need to convert or combine measured levels before entering them, the sound pressure level calculator handles dB arithmetic and unit conversions.

OSHA (the US enforceable Permissible Exposure Limit) uses a 90 dB criterion for an 8-hour shift and a 5 dB exchange rate — every 5 dB louder halves the allowed time. The allowed time is T = 8 / 2^(L−90)/5, the dose is 100 × Σ(C⊂ᵢ/T⊂ᵢ), and the TWA is TWA = 90 + 16.61 × log₁₀(dose/100). OSHA also defines an action level at 85 dB TWA (50 % dose) that triggers a hearing-conservation program.

NIOSH (the recommended, more protective limit) uses an 85 dB criterion and a 3 dB exchange rate — the equal-energy rule, where every 3 dB louder halves the allowed time. Here T = 8 / 2^(L−85)/3, the dose is 100 × Σ(C⊂ᵢ/T⊂ᵢ), and the TWA is TWA = 85 + 10 × log₁₀(Σ(C⊂ᵢ/T⊂ᵢ)). Because NIOSH starts lower and counts loud sound more steeply, the same day almost always lands at a higher dose under NIOSH than under OSHA.

When a result goes over a limit, the tool shows where hearing protection would bring you back under, using the NRR (Noise Reduction Rating) concept. NIOSH recommends de-rating the printed NRR by subtracting 25 % for earmuffs, 50 % for slow-recovery formable plugs, and 70 % for all other (foam) plugs, then subtracting a further 7 dB for A-weighted exposures, to get a realistic field attenuation. The protected level then feeds back into the same dose math. This is education on the concept, not a fitting recommendation.

Workers in industries such as construction, manufacturing, mining, and aviation frequently encounter occupational noise exposures that span several distinct noise environments in a single shift — a variable noise exposure scenario where the multi-row entry approach is essential. The OSHA hearing conservation program (29 CFR 1910.95) requires employers to monitor, notify, and provide audiometric testing once an 8-hour TWA reaches or exceeds the 85 dB action level. The NIOSH criteria document (Publication 98-126) explains why the 3 dB equal-energy exchange rate is scientifically preferred: it reflects that hearing damage is cumulative — the total acoustic energy absorbed by the cochlea, not just peak exposure, is what matters. If your measurement data comes from a personal noise dosimeter, that device already integrates C/T internally; entering its reported dose directly is a quick cross-check of the dosimeter's math. If you want to understand the spectral character of a space before sampling — for example, to confirm whether measured levels are dominated by broadband machinery noise or a tonal source — the noise floor analyzer provides an octave-band breakdown that can inform your measurement strategy.

The 5 dB exchange rate (OSHA) and the 3 dB exchange rate (NIOSH) may sound like a minor technical detail, but they produce dramatically different allowed times at loud levels. At 95 dBA, OSHA’s formula gives an allowed time of 4 hours; NIOSH’s gives roughly 30 minutes. At 100 dBA, OSHA allows 2 hours while NIOSH allows about 15 minutes. The gap widens with every 5 dB increase because the NIOSH rule penalises loud sound more steeply, reflecting the equal-energy principle: doubling the sound energy (a true +3 dB) should halve safe exposure time, regardless of where on the scale you start. The OSHA 5 dB rate does not track equal energy -- it is a regulatory compromise that has remained in the enforceable PEL since 1971.

A common search question is "how long can I listen at 85 dB?" Under NIOSH the answer is 8 hours; under OSHA, 85 dBA sits below the 90 dB criterion so it is not directly restricted by the PEL formula (though it does trigger the OSHA action level and hearing-conservation requirements). This is why NIOSH and many hearing researchers consider the 3 dB rule the safer guide for any listening situation -- occupational or recreational. Enter your own exposures above to see the gap in your specific case. For measuring or combining levels before you enter them, the sound pressure level calculator handles dB arithmetic, and the noise floor analyzer can help characterise the spectral content of an environment.