A decibel (dB) is a logarithmic unit used to measure the intensity of sound, signal strength, and other quantities. Named after Alexander Graham Bell, it expresses ratios on a log scale: every 10 dB increase represents a 10-fold increase in sound intensity.

At what decibel level does hearing damage occur?

Prolonged exposure to sounds above 85 dB can cause hearing damage. At 100 dB, damage can occur in 15 minutes. At 120 dB (pain threshold), immediate damage is possible. Normal conversation is about 60-70 dB.

Why is the decibel scale logarithmic?

The decibel scale is logarithmic because human hearing perceives loudness logarithmically. A sound that is 10 times more powerful sounds only about twice as loud. The logarithmic scale also compresses the enormous range of human hearing (from a pin drop to a jet engine) into manageable numbers.

What Is a Decibel? Sound Level Guide with dB Chart

Definition

A decibel (symbol: dB) is a logarithmic unit that measures the ratio of one value to a reference value. In acoustics, 0 dB is set at the threshold of human hearing (about 20 micropascals). Each 10 dB increase represents a tenfold increase in sound intensity.

dB = 10 × log₁₀(P/P₀) where P₀ is the reference power.

Common Sound Levels

Decibels	Sound Source	Effect
0 dB	Threshold of hearing	Barely perceptible
20 dB	Whisper, rustling leaves	Very quiet
40 dB	Library, quiet office	Quiet
60 dB	Normal conversation	Moderate
70 dB	Vacuum cleaner, traffic	Intrusive
85 dB	Heavy traffic, factory	Damage begins (prolonged)
100 dB	Motorcycle, jackhammer	15 min safe exposure
110 dB	Rock concert	2 min safe exposure
120 dB	Thunder, jet takeoff (300m)	Pain threshold
140 dB	Gunshot, fireworks	Immediate damage risk

Key Decibel Relationships

+3 dB: Doubles the sound intensity (power)
+6 dB: Doubles the sound pressure (amplitude)
+10 dB: Sounds approximately twice as loud to human ears
+20 dB: Sounds roughly 4 times as loud

Beyond Sound: Other Uses of Decibels

Electronics and Telecommunications

Signal strength (WiFi, cellular) is measured in dBm. A WiFi signal at -30 dBm is excellent; at -80 dBm it is weak.

Earthquakes

The Richter scale is logarithmic like decibels. Each whole number increase represents 10 times more ground motion.

History

The decibel is one-tenth of a bel, named after Alexander Graham Bell. The bel proved too large for practical use, so the decibel became the standard. It was originally developed by Bell Telephone Laboratories to quantify signal loss in telephone lines.