Noise Exposure Time Calculator

Estimate maximal occupational noise exposure time from a measured A-weighted sound level using OSHA or NIOSH criteria.

Calculate safe noise exposure time

Enter a steady workplace noise level and select the exposure standard to apply.

Noise Level (dBA)

Exposure Standard

About the noise exposure time calculator

Occupational noise limits connect sound level with the maximum daily duration of exposure. Because the decibel scale is logarithmic, a small increase in dBA represents a large increase in sound energy. Exposure guidance therefore shortens allowable time rapidly as noise rises. This calculator applies the standard exchange-rate equation to estimate a duration for one constant A-weighted noise level. The OSHA permissible exposure limit uses a 90 dBA criterion level for eight hours and a 5 dB exchange rate. Under that approach, every 5 dB increase halves the allowed duration: 90 dBA permits 8 hours, 95 dBA permits 4 hours, and 100 dBA permits 2 hours. The NIOSH recommended exposure limit is more protective. It starts at 85 dBA for eight hours and uses a 3 dB exchange rate, so 88 dBA permits 4 hours, 91 dBA permits 2 hours, and 100 dBA permits only 15 minutes. These estimates assume a relatively steady sound level. Real workdays often involve several tools, machines, and tasks at different levels. In that situation, each exposure contributes a fraction of its allowable daily dose. Safety professionals add those fractions to assess the combined dose rather than treating each segment independently. Impulse or impact noise also needs special attention because a time-weighted average may not represent hazardous peaks. Use a calibrated sound-level meter or personal noise dosimeter whenever decisions affect worker protection. Phone applications can be useful for screening but vary in microphone response and calibration. Measurements should use A-weighting and an appropriate response setting, record the worker's actual position, and include representative operating conditions. Hearing protection does not automatically reduce exposure by the full labeled noise reduction rating; workplace derating and fit are important. This tool is educational and does not replace a workplace noise survey, applicable regulations, or an occupational health program. OSHA rules may impose additional requirements, and local standards can differ. If exposures approach or exceed limits, use the hierarchy of controls: reduce noise at the source, isolate equipment, limit time, provide properly selected hearing protection, train workers, and arrange hearing conservation monitoring with qualified safety personnel.

Noise exposure examples

Noise and standard	Maximum time	Calculation
90 dBA under OSHA	8 hours	OSHA's criterion level permits an eight-hour daily exposure.
100 dBA under OSHA	2 hours	Two 5 dB increases reduce eight hours to two hours.
100 dBA under NIOSH	15 minutes	Five 3 dB increases reduce eight hours to one quarter hour.
94 dBA under NIOSH	1 hour	Three 3 dB increases halve the duration three times.

How to calculate maximal noise exposure

Measure the representative sound level in dBA with a calibrated meter or dosimeter.
Enter the measured level and select either the OSHA limit or NIOSH recommendation.
Select Calculate Safe Exposure to estimate the maximum duration at that constant level.
Combine varying exposures as dose fractions and consult a safety professional when limits may be exceeded.

Noise exposure calculator FAQ

Why do OSHA and NIOSH give different times?

They use different criterion levels and exchange rates. NIOSH begins at 85 dBA and halves time every 3 dB, making its recommendations more protective than OSHA's 90 dBA and 5 dB approach.

What does dBA mean?

dBA is an A-weighted decibel measurement that approximates the frequency sensitivity of human hearing. Occupational standards commonly use it for continuous workplace noise assessment.

Can I add safe times for different noise levels?

No, each period consumes a fraction of the permitted daily dose. Add the exposure-duration-to-allowable-duration fractions and keep the total within the selected standard's limit.

Does hearing protection make any exposure safe?

No, protectors have practical limits and their real attenuation depends on selection, fit, training, and consistent use. Engineering and administrative controls should be considered before relying on personal protective equipment.

Can a phone measure workplace noise accurately?

A phone can help identify a possible problem, but its microphone and calibration may be unsuitable for compliance decisions. Use professional instruments and qualified assessment for hearing conservation planning.