Noise Level and Safe Exposure Calculator
Compare dB levels of common sounds and calculate NIOSH daily exposure time at any level.
Covers workplace, concert, traffic, and power tool noise.
Sound pressure level (SPL) is measured in decibels (dB): a logarithmic unit. Because of this logarithmic scale, every 10 dB increase represents a sound that is 10 times more intense in energy, but only approximately twice as loud to human perception (following the Stevens power law).
The decibel formula:
L (dB) = 10 × log₁₀(I ÷ I₀)
Or in terms of sound pressure:
L (dB) = 20 × log₁₀(P ÷ P₀)
Variable definitions:
- L = sound level in decibels (dB)
- I = sound intensity (W/m²)
- I₀ = reference intensity = 10⁻¹² W/m² (threshold of hearing)
- P = sound pressure (Pa)
- P₀ = reference pressure = 20 μPa (threshold of hearing)
Adding sound sources:
L_combined = 10 × log₁₀(10^(L1/10) + 10^(L2/10))
Two identical sound sources together are only 3 dB louder than one, not double.
Reference sound levels:
| Source | Approximate dB |
|---|---|
| Threshold of hearing | 0 dB |
| Whisper | 30 dB |
| Quiet library | 40 dB |
| Normal conversation | 60 dB |
| Busy restaurant | 75 dB |
| Lawnmower | 90 dB |
| Rock concert | 110 dB |
| Jet engine at 30 m (100 ft) | 140 dB |
| Pain threshold | 130–140 dB |
Safe exposure limits (NIOSH recommended, US):
This is what the calculator above uses: 85 dB for 8 hours, and the allowed time halves for every 3 dB on top.
| SPL | Maximum Daily Exposure |
|---|---|
| 85 dB | 8 hours |
| 88 dB | 4 hours |
| 91 dB | 2 hours |
| 94 dB | 1 hour |
| 97 dB | 30 minutes |
| 100 dB | 15 minutes |
| 103 dB | 7.5 minutes |
| 106 dB | 3.75 minutes |
NIOSH and OSHA do not agree, and the gap is large. OSHA, the enforceable US standard, permits 90 dB for 8 hours and halves the time every 5 dB. NIOSH, the research agency, recommends 85 dB for 8 hours and halves every 3 dB. At 100 dB that is the difference between OSHA’s 2 hours and NIOSH’s 15 minutes: an eightfold gap for the same noise. OSHA is the legal minimum you can be held to, NIOSH is the level the evidence actually supports. If you are choosing for your own ears rather than for a compliance file, use the NIOSH column.
Noise-induced hearing loss is permanent and cumulative. Wear hearing protection at any sustained exposure above 85 dB.
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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