What does dB mean in sound?

dB stands for decibel, a logarithmic unit used to express the ratio of a sound pressure level to a reference level. In acoustics the reference is 20 micropascals (μPa), the threshold of human hearing. Because the scale is logarithmic, each +10 dB increase represents a 10-fold increase in sound intensity (watts per square meter), while human perception judges it as roughly twice as loud.

How loud is 85 decibels?

85 dB is roughly equivalent to heavy city traffic or a busy restaurant kitchen. OSHA and NIOSH guidelines set 85 dB (A-weighted, 8-hour time-weighted average) as the action level where hearing protection should be provided. Prolonged exposure above this level — without ear protection — causes irreversible noise-induced hearing loss over time.

How much louder is 100 dB than 90 dB?

100 dB is 10 dB louder than 90 dB. A +10 dB change represents a 10× increase in physical sound intensity (power per unit area) and is perceived by humans as approximately twice as loud. So 100 dB is 10 times more intense and sounds about twice as loud as 90 dB.

Decibel Guide: What dB Means, Common Sound Levels & Hearing Safety

What Is a Decibel?

A decibel (dB) is one-tenth of a bel, a unit named after Alexander Graham Bell. It expresses a ratio on a logarithmic scale. In acoustics, sound pressure level (SPL) in dB is defined as:

SPL (dB) = 20 × log&sub1;&sub0;(P / P&sub0;)

where P is the measured sound pressure and P₀ = 20 µPa is the reference pressure (the threshold of human hearing at 1 kHz). Because the scale is logarithmic, a doubling of pressure adds only about 6 dB, while a tenfold increase in intensity (power) corresponds to +10 dB.

Common Sound Levels Reference Table

Sound Level (dB)	Example Sound	Effect / Sensation
0	Threshold of hearing	Inaudible to most people
10	Breathing, rustling leaves	Barely perceptible
20	Studio soundproofed room	Very quiet
30	Whisper at 1 m	Quiet
40	Library, quiet office	Low background noise
50	Moderate rainfall	Comfortable
60	Normal conversation at 1 m	Comfortable
70	Busy restaurant, TV	Somewhat intrusive
80	Alarm clock, vacuum cleaner	Annoying; fatigue with long exposure
85	Heavy city traffic, machinery	OSHA/NIOSH hearing protection threshold
90	Lawnmower, power tools	Hearing damage with prolonged exposure
100	Motorcycle, live concert front row	Serious damage within minutes unprotected
110	Rock concert, jackhammer	Pain begins; 2 min max safe exposure
120	Ambulance siren at 1 m	Pain threshold; immediate risk
130	Military jet at 30 m	Severe pain; eardrum rupture risk
140	Jet engine at 5 m, gunshot	Immediate permanent hearing damage

dB Change vs. Perceived Loudness

The human auditory system does not perceive sound linearly. The table below summarizes the relationship between physical intensity ratio, dB change, and perceived loudness change.

dB Change	Intensity Ratio (physical)	Perceived Loudness Change
+1 dB	1.26×	Barely perceptible (just noticeable)
+3 dB	2×	Slightly louder (noticeable to trained ear)
+6 dB	4×	Clearly louder
+10 dB	10×	Approximately twice as loud (to human perception)
+20 dB	100×	Approximately four times as loud
+30 dB	1,000×	Approximately eight times as loud
−10 dB	0.1×	Approximately half as loud
−20 dB	0.01×	Approximately one-quarter as loud

A-Weighting (dBA)

Human hearing is not equally sensitive at all frequencies. We are most sensitive around 1–4 kHz and less sensitive to very low and very high frequencies. A-weighting (dBA) applies a frequency filter that mimics human sensitivity, making dBA readings better correlate with perceived loudness and hearing damage risk. Most occupational health regulations specify limits in dBA. The common reference points (85 dBA, 90 dBA) are A-weighted values.

Hearing Damage and Safe Exposure Times

NIOSH (National Institute for Occupational Safety and Health) recommends a maximum of 8 hours at 85 dBA. For every 3 dB increase, the safe exposure time halves:

85 dBA — 8 hours max
88 dBA — 4 hours max
91 dBA — 2 hours max
94 dBA — 1 hour max
100 dBA — 15 minutes max
106 dBA — less than 4 minutes
110+ dBA — risk of immediate damage

Sound and energy share units in some contexts — use our energy converter to convert between joules, watts, and related units.