Noise Exposure Calculator
Build your day as rows of sound level (dBA) and duration, and this tool computes your cumulative daily noise dose (%) and Time-Weighted Average (TWA) under both the OSHA (90 dB criterion, 5 dB exchange rate) and NIOSH (85 dB criterion, 3 dB exchange rate) methods, with a compliance verdict and hearing-protection guidance.
ℹ This is pure arithmetic on the numbers you type in — not a measurement and not an occupational-health determination. The result is only as good as your level data, which should come from a calibrated sound-level meter or dosimeter, not a guess or a browser-mic estimate. The OSHA and NIOSH formulas, criteria and exchange rates here are the published standards (cited below), but a real exposure assessment depends on measurement method, mic placement, microphone calibration and how a full shift is sampled. Treat this as guidance for understanding the math — for compliance, an OSHA-recordable determination, or any legal/medical decision, consult a qualified industrial hygienist. Everything is computed locally; nothing is uploaded.
Add one row per distinct activity or noise level in your shift. Enter the steady A-weighted level in dB(A) and how long you are exposed to it. Durations can be in hours or minutes (per-row unit selector).
Total exposure time: 0 h 0 min.
Results
How It Works
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.
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.