The 3 dB rule: sound energy and exposure time

3 dB and 10 dB describe different-sized changes

Decibels are logarithmic. An increase of about 3 dB doubles sound energy; an increase of 10 dB corresponds to ten times the energy. This is an energy comparison, not a claim that 3 dB sounds twice as loud.

For comparable measurements, subtract the two levels to find the change. Do not add their decibel values together or treat a simple arithmetic average as an energy average. The meter calculates its session average from captured energy.

Why the reference time halves

The NIOSH occupational reference uses 85 dBA over eight hours and a 3 dB exchange rate. For each 3 dB increase, the corresponding duration halves.

A worked calculator example

For a suitably measured constant level of 91 dBA, the level is 6 dB above 85 dBA. That is two 3 dB steps, so the reference time is 8 ÷ 2 ÷ 2 = 2 hours. The calculator uses T = 8 × 2^((85 − L) / 3) hours.

Enter an appropriate measured A-weighted level. The calculator is independent of the browser meter; it does not verify your microphone or automatically turn its estimate into a valid exposure assessment.

A short run is not your daily dose

These durations illustrate an occupational reference, not a personal guarantee of safety. Daily exposure combines periods at different levels; a quiet interval does not cancel earlier loud exposure. A short browser sample can miss changing tasks and impulse sounds. Use a suitable sound level meter or dosimeter for an exposure assessment.

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