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Methodology
Every number on this site is a typical, published A-weighted value — not a measurement of your specific situation. Here is exactly where the figures come from and how the calculators work.
Where the levels come from
Reference levels are drawn from published data by the National Institute for Occupational Safety and Health (NIOSH), the Occupational Safety and Health Administration (OSHA), the Centers for Disease Control and Prevention (CDC), the WHO Environmental Noise Guidelines, and the American Speech-Language-Hearing Association (ASHA). Where sources differ, we use a representative mid-range value and say so.
The formulas we use
| Quantity | Formula |
|---|---|
| Sound pressure level | L = 20 × log₁₀(p / 20µPa) |
| Energy ratio between two levels | 10^((L₁ − L₂) / 10) |
| Perceived loudness ratio | 2^((L₁ − L₂) / 10) |
| Combining sources | L = 10 × log₁₀(Σ 10^(Lᵢ / 10)) |
| Distance attenuation (point source) | L₂ = L₁ − 20 × log₁₀(d₂ / d₁) |
| NIOSH safe time | 8 h ÷ 2^((L − 85) / 3) |
| OSHA permissible time | 8 h ÷ 2^((L − 90) / 5) |
| Protection de-rating (OSHA) | effective ≈ (NRR − 7) ÷ 2 |
Known limitations
- Real levels vary. Distance, room acoustics and the specific model can move a figure several dB in either direction.
- The online meter is uncalibrated. Phone microphones apply automatic gain control; treat readings as ± 3–6 dB indicators, not evidence.
- Perceived-loudness ratios are approximate. The “10 dB ≈ twice as loud” rule holds around mid-levels and mid-frequencies but is not exact.
- Noise-law figures are educational. Local ordinances are what legally apply; always check yours.
Last reviewed 2026-08-11. Found an error? We want to fix it — see the about page for how to reach us.