Noise Exposure Time Calculator (safe hours per day by dBA, NIOSH and OSHA)

Understanding the noise exposure time calculator — concept and principle

This calculator shows how long you can be exposed to a given noise level each day before reaching the recommended limit, and your daily noise dose. It compares the US NIOSH recommendation with the less protective OSHA legal limit. Workers, safety officers, musicians and anyone using loud tools can use it to plan hearing protection.

Each +3 dB halves the time: with the default inputs the result is dose 200% (2 h at 94 dBA).

How it is calculated

NIOSH allowed time (min) = 480 ÷ 2^((L − 85) ÷ 3)

OSHA allowed time (min) = 480 ÷ 2^((L − 90) ÷ 5)

Daily dose (%) = exposure time ÷ allowed time × 100

L is the A-weighted sound level in dBA at the ear.
A dose of 100% or more exceeds the limit. For several noise levels in a day, add the doses.
No exposure is allowed above 140 dBA.

The principle

Decibels are logarithmic: every 3 dB increase doubles the sound energy. NIOSH uses this equal-energy rule, so each 3 dB rise halves the safe time from 8 hours at 85 dBA. OSHA uses a 5 dB exchange rate and a 90 dBA base, which allows much longer exposure at high levels. Hearing damage from noise depends on the total sound energy reaching the inner ear over time, which is why dose adds up across the day.

Worked example

Default inputs: 94 dBA for 2 hours.

NIOSH time = 480 ÷ 2^((94 − 85) ÷ 3) = 480 ÷ 2³ = 60 min = 1 h 00 min.
NIOSH dose = 120 ÷ 60 × 100 = 200% → within limit No.
OSHA time = 480 ÷ 2^((94 − 90) ÷ 5) = 480 ÷ 1.741 = 275.7 min = 4 h 36 min.
OSHA dose = 120 ÷ 275.7 × 100 = 44%.

How to read the result

Where does your result fall?

A NIOSH dose above 100% means a raised risk of permanent noise-induced hearing loss over a working life. Reduce exposure time, lower the noise at its source or wear hearing protection. Ringing in the ears or muffled hearing after noise are warning signs.

Common mistakes

Using a phone app reading as exact; calibrated meters are more accurate.
Forgetting off-work noise such as concerts, motorbikes or headphones.
Assuming that being within the OSHA limit means hearing is safe.

Keep in mind: This is general information, not a hearing assessment. Workplace exposure should be measured and managed under local regulations; see a doctor or audiologist about hearing loss or tinnitus.

Frequently asked questions

How loud is 85 dBA?

Roughly heavy city traffic or a food blender; it is the NIOSH 8-hour limit.

Why are NIOSH and OSHA different?

NIOSH gives a health-based recommendation; OSHA's legal limit dates from older standards and is less protective.

Do earplugs reduce the dose?

Yes. Properly fitted protection lowers the level reaching the ear, but real-world reduction is often less than the label rating.

Sources: NIOSH, Criteria for a Recommended Standard: Occupational Noise Exposure, Revised Criteria 1998, DHHS (NIOSH) Publication No. 98-126 · OSHA, Occupational Noise Exposure, 29 CFR 1910.95

Checked 9 Nov 2026. NIOSH, Criteria for a Recommended Standard: Occupational Noise Exposure, Revised Criteria 1998, DHHS (NIOSH) Publication No. 98-126, Chapter 1 (REL 85 dBA 8-h TWA, 3-dB exchange rate, daily dose formula, 140 dBA ceiling) and Chapter 2 (OSHA 90 dBA, 5-dB exchange rate).

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