Enter the sound levels a worker is exposed to and for how long. Get the noise dose and 8-hour time-weighted average (TWA) under both OSHA and NIOSH criteria — instantly, free, no signup.
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Add one row per noise level during the shift. Levels below 80 dBA are excluded from the dose, per OSHA and NIOSH threshold rules.
Action level exceeded — hearing conservation program required
Exceeds NIOSH REL (85 dBA TWA)
A dose of 100% equals the full allowable daily exposure: an 8-hour TWA of 90 dBA under OSHA (29 CFR 1910.95) or 85 dBA under NIOSH. OSHA’s action level — 50% dose, 85 dBA TWA — triggers a mandatory hearing conservation program.
How long a worker can be exposed at a constant level before reaching 100% dose. OSHA halves the time every 5 dB; NIOSH, using newer hearing-damage research, halves it every 3 dB — which is why the two diverge so sharply at high levels.
| Sound level (dBA) | OSHA allowable time | NIOSH allowable time |
|---|---|---|
| 80 dBA | 32 hrs | 25 hr 24 min |
| 85 dBA | 16 hrs | 8 hrs |
| 90 dBA | 8 hrs | 2 hr 31 min |
| 95 dBA | 4 hrs | 47.6 min |
| 100 dBA | 2 hrs | 15 min |
| 105 dBA | 1 hr | 4.7 min |
| 110 dBA | 30 min | 1.5 min |
| 115 dBA | 15 min | 28 sec |
Noise dose expresses a day’s total exposure as a percentage of the allowable maximum. For each period at a constant level, the time actually spent is divided by the time allowed at that level, and the fractions are summed: D = 100 × (C₁/T₁ + C₂/T₂ + …). Under OSHA, the allowed time is T = 8 / 2^((L − 90) / 5) hours; NIOSH replaces 90 with 85 and the 5 dB exchange rate with 3 dB.
The 8-hour time-weighted average converts that dose back into a single equivalent level: TWA = 90 + 16.61 × log₁₀(D/100) for OSHA, or 85 + 9.97 × log₁₀(D/100) for NIOSH. A 100% dose always corresponds to a TWA equal to the criterion level. Because the scale is logarithmic, small level changes matter enormously — at 100 dBA, OSHA allows 2 hours of exposure and NIOSH just 15 minutes.
This calculator is ideal for preliminary assessments and ongoing monitoring. For enforcement-grade documentation, OSHA requires measurements from a calibrated Type 2 (or better) sound level meter or dosimeter — see our guides to OSHA noise limits, meter calibration, and the full OSHA standard.
Use our free online decibel meter to measure A-weighted sound levels in your workplace — then plug them straight into this calculator. No download required.
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