A decibel (dB) is a logarithmic unit of sound pressure level relative to the threshold of human hearing. Because it is logarithmic, every 10 dB increase represents a tenfold increase in sound intensity, and roughly a doubling of perceived loudness.

Why is the decibel scale logarithmic?

Human hearing spans an enormous range of intensities, from the faintest audible sound to a painfully loud one — a ratio of about a trillion to one. A logarithmic scale compresses that range into manageable numbers, so 0 dB is the hearing threshold and 120 dB is near the pain threshold.

At what level does sound damage hearing?

Prolonged exposure above 85 dB can cause permanent hearing loss. The NIOSH rule halves safe exposure time for every 3 dB increase: 85 dB is safe for 8 hours, 88 dB for 4 hours, 91 dB for 2 hours, and so on. Above about 120 dB, damage can be immediate.

How does distance affect decibel level?

Sound pressure level drops by about 6 dB each time the distance from a point source doubles, following the inverse-square law. So a 100 dB machine measured at 1 metre is about 94 dB at 2 metres and 88 dB at 4 metres in free field conditions.

Can I add decibels by simple arithmetic?

No. Because decibels are logarithmic, two equal sources do not double the number — they add about 3 dB. Two 80 dB sources together produce roughly 83 dB, not 160 dB. Combining different levels requires logarithmic addition, not ordinary sums.

What is the Decibel (dB) Reference Table?

A reference table of common sound pressure levels in decibels, from the threshold of hearing to a jet engine, with NIOSH safe-exposure times. Enter a dB value to see what it sounds like and how long it is safe to hear. Runs in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Decibel (dB) Reference Table

Name: Decibel (dB) Reference Table
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Raw decibel readings from a sound meter app are hard to interpret without context. Is 72 dB safe for a whole shift? What does 95 dB actually sound like? This reference table anchors common dB values to familiar everyday sounds and shows the NIOSH-recommended safe daily exposure time at each level, so a meter reading turns into something you can act on.

How the decibel scale works

Sound pressure level in decibels (dB SPL) is measured relative to the threshold of human hearing (approximately 20 micropascals). Because the scale is logarithmic, equal numeric steps represent multiplicative changes in intensity:

+10 dB  = 10× the sound intensity, ≈ 2× perceived loudness
+3 dB   ≈ doubling of intensity (two equal sources add ~3 dB, not double the number)
−6 dB   per doubling of distance from a point source (inverse-square law)

This is why two identical 80 dB machines running together measure about 83 dB, not 160 dB. And why a loudspeaker that sounds twice as loud is actually about 10 dB higher on the meter.

NIOSH 3 dB exchange rate for exposure

NIOSH (the US National Institute for Occupational Safety and Health) uses a 3 dB exchange rate: safe daily exposure time halves for every 3 dB increase above 85 dB. OSHA uses a 5 dB exchange rate (more permissive), but audiologists and public health bodies generally prefer the tighter NIOSH standard.

Level (dB)	NIOSH safe daily exposure
85	8 hours
88	4 hours
91	2 hours
94	1 hour
97	30 minutes
100	15 minutes
103	7.5 minutes
110	~1 minute
120+	Immediate risk

Common sound levels for reference

0–20 dB — threshold of hearing, anechoic chamber, rustling leaves
30 dB — quiet library, soft whisper at 1 metre
50–60 dB — normal conversation, office background noise
70 dB — vacuum cleaner at 3 metres, busy restaurant
85 dB — heavy road traffic, motorcycle, lawnmower — damage risk begins here with extended exposure
95–100 dB — nightclub, power tools, hearing protection recommended
110 dB — live concert near the speakers, car horn at 1 metre
120 dB — rock concert at front row, ambulance siren at close range, near pain threshold
130–140 dB — jet engine at 30 metres, gunshot, immediate hearing damage

Distance and dB: the inverse-square law

Moving away from a sound source reduces the level predictably: doubling the distance drops the reading by approximately 6 dB. A machine measuring 100 dB at 1 metre is about 94 dB at 2 metres and 88 dB at 4 metres (in an open, non-reflective environment). In a reverberant room the drop is less pronounced because reflected sound maintains the level.

Enter a dB value to see the nearest real-world reference and whether your exposure duration is within safe limits.