How to Read a Decibel Chart
What these charts are
A decibel chart lists familiar sounds — a refrigerator hum, city traffic, a siren — next to typical sound-level values. Government references publish them because the numbers are otherwise hard to develop intuition for. Reading one correctly requires knowing four things the chart itself rarely spells out.
1. The scale is logarithmic
As covered in what is a decibel, each 10 dB step is a tenfold change in sound energy and is heard as roughly a doubling of loudness. The distance from 60 dB to 90 dB is not "half again louder" — it is a thousandfold difference in energy. Chart entries that look close numerically can be far apart physically. The National Park Service's acoustics page explains the amplitude scale and gives representative values for natural and human-made sounds.
2. The values are usually A-weighted
Most charts state levels in dBA — sound pressure filtered to approximate the ear's frequency response, which is less sensitive at the extremes of the spectrum. A dBA figure and an unweighted figure for the same source can differ, particularly for low-frequency sound. If a chart doesn't say, assume dBA for environmental noise.
3. Distance is part of the number
A sound level is meaningful only at a stated distance. Sound spreading in open space drops roughly 6 dB with each doubling of distance from the source, so "a lawn mower" as heard by its operator and as heard across the street are different chart entries. Good charts specify the measurement position; when comparing your situation to a chart, compare distances too.
4. Level and duration are read together
Charts of hearing-health interest typically pair levels with exposure time, because the research on noise and hearing treats the two jointly — brief and sustained exposure to the same level are different situations. The mechanism, and the reference charts themselves, are laid out by the NIDCD's page on noise-induced hearing loss, and the WHO's fact sheet on deafness and hearing loss covers safe-listening concepts at the population level. Those sources — not a summary of them — are the right place to read the specific figures, since they carry the context the numbers depend on.
What a chart cannot tell you
A chart describes typical sources; it does not measure your environment (sound level meters and meter apps exist for that) and it cannot assess your hearing. Questions about personal exposure, hearing changes, or hearing protection selection belong with an audiologist or occupational-health professional, who can measure rather than estimate.
Where to go next
For how the same dB notation shows up inside digital audio at negative values, see LUFS vs. dBFS. For dB figures printed on headphone boxes — a different usage again — see headphone impedance and sensitivity.