Safe Noise Exposure Time Calculator
How long a noise level is safe before hearing damage starts, using the NIOSH 3 dB rule, and how much time earplugs or muffs actually buy you.
Noise-induced hearing loss is one of the most common occupational hazards and recreational risks worldwide.
NIOSH (National Institute for Occupational Safety and Health) recommends a maximum exposure of 85 decibels (dB) for 8 hours. For every 3 dB increase above 85 dB, the safe exposure time is cut in half.
Safe exposure time formula (NIOSH):
T = 8 / (2 ^ ((dB - 85) / 3)) hours
Common noise levels:
- Normal conversation: 60-70 dB (safe)
- Vacuum cleaner: 70 dB (safe)
- City traffic from inside a car: 80-85 dB (8 hours at the top of that range)
- Lawn mower: 90 dB (about 2.5 hours)
- Concert or nightclub: 100-110 dB (minutes only)
- Chainsaw: 110 dB (about 1.5 minutes)
- Fireworks at close range: 140-160 dB (immediate damage)
OSHA (Occupational Safety and Health Administration) uses a slightly more lenient standard with a 5 dB exchange rate. NIOSH uses a 3 dB exchange rate, which is considered more protective and is used in this calculator.
Hearing protection, and why this page uses smaller numbers than the packet The Noise Reduction Rating printed on a box of earplugs is measured in a laboratory, on a subject whose plugs were fitted by a technician. Real people roll foam plugs badly and push them in half way, and muffs leak around the arms of glasses. NIOSH therefore derates the labelled figure: halve it for foam plugs, take a quarter off for muffs. This calculator uses the derated numbers, so it gives roughly 12 dB for foam where the box claims 25.
That is not pessimism, it is the difference between a calculator that tells you the truth about a 95 dB workshop and one that tells you what you would like to hear. Doubling up plugs under muffs does not add the two ratings together either. You gain about 6 dB over the better of the two, not the 29 that adding them would suggest, because bone conduction sets a floor on what any protector can achieve.
Key facts:
- Hearing damage is cumulative and permanent.
- Ringing in the ears (tinnitus) after exposure is a warning sign.
- Regular hearing checks are recommended for anyone exposed to loud environments.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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