What this calculator does
Hearing damage depends on both how loud a sound is and how long you are exposed to it, and the two trade off exponentially. Every few decibels halves the time you can safely spend in it.
Which few decibels depends on the standard. NIOSH uses a 3 dB exchange from an 85 dB baseline, so 95 dBA allows only 47 minutes. OSHA uses a 5 dB exchange from 90 dB, which permits 4 hours at the same 95 dBA.
The formula
The permitted time halves for every exchange-rate increment above the reference level. NIOSH uses 85 dBA with a 3 dB exchange; OSHA uses 90 dBA with a 5 dB exchange.
| Term | Meaning |
|---|---|
| Exchange rate | How many decibels halve the permitted exposure time. |
| dBA | A-weighted decibels, adjusted to reflect how human hearing responds. |
| NIOSH and OSHA | A research body and a regulator, using different and incompatible standards. |
The inputs explained
| Field | What to enter |
|---|---|
| Noise level (dBA) | Noise level in A-weighted decibels. |
| Standard | Which standard to apply. The two give substantially different answers. |
When to use it
Assessing a workplace
Exposure limits determine when hearing protection becomes mandatory.
Understanding concert or power tool exposure
Loud leisure activity accumulates the same way work exposure does.
Comparing the two standards
The same measurement yields very different permitted times.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How fast does permitted time fall?
Five noise levels and their permitted daily exposure.
| Noise level | Maximum daily exposure | Reference level |
|---|---|---|
| 85 dBA | 8 h 0 min | 85 dBA for 8 hours |
| 90 dBA | 2 h 31 min | 85 dBA for 8 hours |
| 95 dBA | 0 h 47 min | 85 dBA for 8 hours |
| 100 dBA | 0 h 15 min | 85 dBA for 8 hours |
| 110 dBA | 0 h 1 min | 85 dBA for 8 hours |
Questions
Why do NIOSH and OSHA disagree?
OSHA's 5 dB exchange dates from the 1970s and is a regulatory compromise. NIOSH's 3 dB exchange reflects the equal-energy principle, which matches the physics better and is used by most other countries. NIOSH is the more protective of the two.
Why does 3 dB halve the time?
Because a 3 dB increase doubles the sound energy. If damage tracks total energy received, then doubling the intensity should halve the permitted duration, which is exactly what the 3 dB exchange encodes.
Does hearing protection extend the time?
Yes, by its rated attenuation, though real-world reduction is typically well below the laboratory rating. Fit matters enormously, and protection worn incorrectly may provide very little.
Is quiet time afterwards enough to recover?
Partial recovery from temporary threshold shift happens, but repeated exposure causes cumulative permanent damage. Time away from noise helps and does not undo what has already occurred.
For another exposure limit, see the hand sanitizer recipe calculator. For sleep quality, see the sleep debt calculator.