How long at 85, 90, 95 or 100 dBA?

A reference dose, not a guaranteed safe time

Using the NIOSH occupational model: 85 dBA corresponds to 8 hours; 90 dBA to about 2 hours 31 minutes; 95 dBA to about 48 minutes; and 100 dBA to 15 minutes. Each reaches the same reference dose. Injury does not begin at a predictable countdown, and a lower dose does not guarantee safety. [1]

NIOSH’s reference was developed for workplace exposure over a working lifetime. It does not protect every individual from every hearing effect and is not a general recreational listening recommendation. Lower sound levels and less exposure are preferable. [1]

Compare the reference times

Time to reach 100% of the NIOSH occupational daily reference dose
Average level (dBA)	Calculated reference time
85	8 hours
88	4 hours
90	About 2 hours 31 minutes
91	2 hours
94	1 hour
95	About 48 minutes
97	30 minutes
100	15 minutes
103	7 minutes 30 seconds
106	3 minutes 45 seconds
109	About 1 minute 53 seconds

Times are calculated using an 85 dBA, eight-hour reference and a 3 dB exchange rate. Values are rounded for display. They assume a steady average exposure and do not model hearing-protector fit, other noise during the day, or impulse sounds. [2]

If you are already in a loud setting, take protective action now. These figures are not a reason to delay using hearing protection.

Why three decibels changes the time

For the same reference dose, every 3 dB increase halves the duration: 85 dBA for eight hours, 88 dBA for four, and 91 dBA for two. Small numerical changes in decibels can represent large changes in sound energy. [2]

T = 480 × 2^((85 − L) / 3), where T is the reference time in minutes and L is the average level in dBA.

For example, 90 dBA is five decibels above 85. The calculated duration is about 151 minutes. This is why 90 dBA does not have the same duration as the 91 dBA row.

Try different levels and durations in the interactive exposure calculator. A phone’s peak reading is not a sustained average and should not be entered as one.

Different exposures add together

For each steady exposure, divide the actual duration by the reference duration at that level. Add the fractions, then multiply by 100 to express the comparison as a percentage. This is an educational example, not a personal dosimeter assessment. [2] [1]

Illustrative unprotected exposures in one day
Activity segment	Fraction of reference dose
30 minutes at 94 dBA	30 ÷ 60 = 0.50 (50%)
15 minutes at 97 dBA	15 ÷ 30 = 0.50 (50%)
Combined comparison	0.50 + 0.50 = 1.00 (100%)

The two segments reach the full reference together even though neither does alone. Work, hobbies, and entertainment can contribute to the same day’s exposure. Moving into quiet reduces further exposure; it does not reset the accumulated dose.

When this calculation is the wrong tool

Gunfire, fireworks, or blasts: short peaks can cause immediate injury and are not adequately represented by this timer.
Unknown or rapidly varying levels: one spot reading may not represent the whole activity.
Children or individual medical decisions: the occupational reference is not a personalized listening allowance.
Hearing-protector performance: a package rating cannot establish your protected level.
Legal compliance: this educational calculation is not an assessment against workplace regulations.

Use a professional exposure assessment where necessary, and involve an audiologist or ENT physician when hearing symptoms or individual risk need evaluation. [3] [4] [1]

Turn the comparison into a prevention plan

Choose a quieter source when possible. Increase distance, shorten time, and use appropriate protection. At work, ask about exposure monitoring and the hearing conservation program. At an event, identify quiet areas before it starts. [5]

Read how to protect your hearing and how to compare earplugs and earmuffs. If your hearing suddenly changes, seek immediate medical care rather than using the calculation to reassure yourself. [6]

Sources and editorial information

Published by Hearing Is. Sources checked October 7, 2026. AI assistance was used in preparing this guide. No independent clinical review is claimed.

Educational information, not an individual diagnosis, treatment plan, or occupational compliance assessment. Read our editorial standards and medical disclaimer.