Decibels and Safe Listening Time: Noise Exposure Limits and Adding Sound Levels
October 29, 2026
The decibel (dB) is a logarithmic unit. Every increase of 10 dB represents a tenfold increase in sound power (and sounds roughly twice as loud to the ear), and every 3 dB represents a doubling of sound power. The A-weighted scale (dBA) approximates human hearing sensitivity.
The US National Institute for Occupational Safety and Health (NIOSH) recommends a limit of 85 dBA for 8 hours a day, with a 3 dB exchange rate: for each 3 dB increase, the permissible time is halved. (OSHA uses 90 dBA with a 5 dB exchange rate for legal limits.)
Skip the math and get your answer instantly:
Open the Scientific Calculator →Safe Exposure Times
Time = 8 hours ÷ 2^((level − 85) ÷ 3). At 88 dBA: 4 hours. At 91 dBA: 2 hours. At 94 dBA: 1 hour. At 97 dBA: 30 minutes. At 100 dBA: 15 minutes. At 106 dBA: under 4 minutes. A typical lawn mower produces about 90 dBA, a motorcycle 95 to 100, a rock concert or club 100 to 110, and headphones at maximum volume can reach 100 to 105. A conversation is about 60 dBA, and city traffic 70 to 85. Damage to hearing from noise is cumulative and permanent; ringing in the ears after exposure is a warning sign.
| Sound level (dBA) | Maximum daily time (NIOSH) | Example |
|---|---|---|
| 85 | 8 hours | Heavy city traffic |
| 88 | 4 hours | Food blender |
| 91 | 2 hours | Lawn mower (about 90) |
| 94 | 1 hour | Loud power tool |
| 100 | 15 minutes | Motorcycle, loud headphones |
| 106 | 3.75 minutes | Concert front rows |
Adding Sound Levels
You cannot add decibels directly. Convert to power, add, and convert back: L = 10 × log₁₀(10^(L₁/10) + 10^(L₂/10)). Two 80 dB sources together: 10 × log₁₀(2 × 10⁸) = 83 dB. Ten identical 80 dB sources: 90 dB. A 80 dB source and a 70 dB source: 10 × log₁₀(10⁸ + 10⁷) = 80.4 dB, barely louder than the louder one alone. A 90 dB source plus a 85 dB: 91.2 dB. The loudest source dominates, so reduce it first.
Protecting Your Hearing
Use earplugs or earmuffs rated for the noise (noise reduction rating NRR in the US; actual reduction is often about half of the rating in the field). Keep headphone volume to 60% or less of the maximum and take breaks: a common rule is 60/60, no more than 60 minutes at 60% volume. Move away from speakers; each doubling of distance from a source drops the level by 6 dB in an open space. Phones and smartwatches can show weekly exposure. If you have persistent ringing or trouble following conversations, see a hearing professional.
Frequently Asked Questions
What does a 3 dB increase mean?
A doubling of sound power, and half the safe exposure time under NIOSH.
How long can I listen at 100 dBA?
About 15 minutes per day by NIOSH.
How loud are two 80 dB sources?
About 83 dB.
How much does moving away reduce noise?
About 6 dB per doubling of distance in open space.
What is the 60/60 rule for headphones?
No more than 60 minutes at 60% volume.