How Loud Is 70 Decibels? The One Environmental Criterion

The 1974 EPA levels document identified a 24-hour exposure level of 70 decibels as the environmental noise level that would prevent any measurable hearing loss over a lifetime. Alongside it, the same document identified 55 decibels outdoors and 45 decibels indoors as levels preventing activity interference and annoyance.

The EPA's own summary is unusually clear about what kind of number this is. The levels, it says, are not single event or peak levels; they represent averages of acoustic energy over periods of time such as 8 or 24 hours, and over long periods such as years.

It is also careful about status. The document states that it does not constitute a standard, specification or regulation. It was published to give state and local governments a basis for their own judgments, to be weighed alongside cost, local conditions and available means of control.

Most content that quotes this figure treats 70 dB as a line you cross. The source says the opposite. Because the criterion is an energy average, a loud hour and a quiet evening combine; the EPA explicitly notes that occasional higher noise levels are consistent with a 24-hour energy average of 70 decibels so long as sufficient relative quiet is experienced for the remaining period.

This is the same logic that underlies occupational exposure criteria, where a level is always paired with an averaging period and an exchange rate. A level without a period is not an exposure criterion at all.

It follows that a phone showing 70 tells you almost nothing about your day. Two people can both see 70 on a display and have completely different 24-hour energy totals.

The EPA figure is environmental and covers the whole day. Occupational criteria cover a work shift and start higher. NIOSH recommends 85 dBA as an 8-hour time-weighted average with a 3-decibel exchange rate; OSHA's permissible exposure level is 90 dBA over 8 hours, with an action level of 85 dBA and a 5-decibel exchange rate.

These are different instruments for different purposes, built from different datasets and different acceptable-risk judgments. The gap between 70 and 85 or 90 is not a contradiction; it is the difference between protecting a whole population across a lifetime of all-day exposure and regulating a workforce across a shift.

None of these figures can be read as a personal safety threshold, and we do not present them that way.

This is the part of the scale where everyday environments actually sit, and where a consumer device is most usable — signal comfortably above microphone self-noise, generally below the level where automatic gain control intervenes.

Even here the honest framing holds. Uncalibrated, our meter reports an A-weighted digital level in dBFS, which is relative to digital full scale rather than to sound pressure. A one-time local calibration against a trusted reference reading lets it report an estimated dBA figure instead. Neither number is traceable, and neither can produce a 24-hour energy average unless you actually measure across the 24 hours.