Decibel SPL Safe Exposure Calculator
How long you can safely listen at a given dB SPL level before hearing damage risk โ per NIOSH (3 dB exchange) and OSHA (5 dB exchange) limits.
Result
- Sound level85 dB SPL
- Reference standardNIOSH REL (85/3)
- Baseline (8 h limit)85 dB SPL
- Exchange rate3 dB per halving
- Safe exposure8.00 hours
Step-by-step
- Safe time T = 8 ร 2^((85 โ L) / 3)
- T = 8 ร 2^((85 โ 85) / 3) = 8.0000 hours.
- Equivalent: 8.00 hours.
How to use this calculator
- Measure or estimate the dB SPL of your environment.
- Pick NIOSH (stricter, recommended) or OSHA (US legal limit).
- Read safe exposure time.
About this calculator
Hearing damage risk follows a logarithmic dose curve: every 3 dB louder (NIOSH) or 5 dB louder (OSHA) halves the safe listening time. NIOSH's 3 dB rule reflects the equal-energy principle used worldwide; OSHA's 5 dB rule is a US occupational compromise. Both standards anchor at 8 hours and use the A-weighting curve that approximates human hearing sensitivity.
What this calculator does
This calculator returns how long you can safely be exposed to a given dB SPL level before risking permanent hearing damage, using either the NIOSH Recommended Exposure Limit (85 dBA / 8 hours / 3 dB exchange rate โ the hearing-conservation standard adopted by ISO 1999 and most of the world) or the US OSHA Permissible Exposure Limit (90 dBA / 8 hours / 5 dB exchange rate โ the legally enforced US workplace limit). The 3 dB rule reflects the equal-energy principle: every doubling of acoustic energy halves the safe time. The 5 dB rule is a US occupational compromise that allows more exposure per dB.
How it works โ the formula
T_safe (hours) = 8 ร 2^((L_base โ L_measured) / ER)
NIOSH: L_base = 85 dBA, ER = 3 dB
OSHA: L_base = 90 dBA, ER = 5 dBThe exposure-time equation is the canonical noise-dose halving rule. NIOSH uses a 3 dB exchange rate because hearing damage scales with total acoustic energy and 3 dB is a doubling of sound power. OSHA's 5 dB rate is historical and less protective. At 88 dBA the NIOSH calculator returns 4 h; OSHA returns ~6.06 h for the same level โ that gap is the entire reason audiologists prefer NIOSH.
Worked examples
- Inputs:
- level = 60 dB SPL, standard = NIOSH
- Output:
- T_safe โ 2048 hours (~85 days continuous โ effectively unlimited)
Well below baseline; no hearing-conservation concern.
- Inputs:
- level = 95 dB SPL, standard = NIOSH
- Output:
- T_safe = 8 ร 2^((85โ95)/3) โ 0.79 h โ 47 minutes
Wear hearing protection for any extended use.
- Inputs:
- level = 110 dB SPL, standard = NIOSH
- Output:
- T_safe โ 1.5 minutes
Damage occurs in minutes; NRR-25 earplugs would extend safe time ~5.6 hours.
When to use this vs other tools
Use this for hearing-conservation planning. For sound-level math or musical frequencies, the related tools below specialize.
- Decibel Calculator
Use to convert between dB and linear ratios for power and amplitude โ the underlying math behind every SPL figure.
- Wavelength Frequency Calculator
Use when you need the wavelength of a sound โ informs speaker/microphone placement and room-mode calculations.
- Frequency Unit Converter
Use to convert between Hz, kHz, and MHz when working across audio (kHz) and RF (MHz) bands.
Authority note
NIOSH 98-126 codifies the 85 dBA / 8 h / 3 dB-exchange Recommended Exposure Limit used worldwide for hearing conservation. The competing OSHA Permissible Exposure Limit (29 CFR 1910.95) is also computed here for US-workplace-compliance contexts.
Limitations
- Dose-based; impulse/peak noise (gunshots, drop-hammer) is a separate hazard not modeled.
- Assumes A-weighted SPL โ pure C-weighted readings overstate the perceived loudness used here.
- Hearing-protection device NRR ratings need a real-world derating (~50% of label) per NIOSH guidance.
- Cumulative exposure across the day combines additively; this tool computes a single-level allowance only.
This tool is for general hearing-conservation planning. Workplaces subject to OSHA must follow the 29 CFR 1910.95 standard; consult an audiologist for medical assessment after suspected overexposure.