Decibel (dB) & Sound Level Calculator
Calculate sound levels in decibels, convert between dB and intensity, and understand what different noise levels mean for your hearing health.
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Decibels and Sound Guide
The Decibel Scale
The decibel (dB) is a logarithmic unit. dB = 10 × log₁₀(I/I₀), where I₀ = 10⁻¹² W/m² (threshold of human hearing). Because it is logarithmic: +10 dB = 10× more power/intensity. +3 dB ≈ 2× more power. +6 dB ≈ 4× more power. Common levels: 0 dB (threshold of hearing), 30 dB (quiet bedroom), 60 dB (normal conversation), 85 dB (heavy traffic), 100 dB (nightclub), 120 dB (jet engine at 100m), 140 dB (threshold of pain).
Combining Sound Levels
Two identical sound sources at 90 dB together produce 93 dB — not 180 dB. This is the logarithmic addition: total = 10 × log₁₀(10^(dB1/10) + 10^(dB2/10)). Two levels equal produce 3 dB more. Two levels 10 dB apart: the combined level is essentially the louder one (within 0.4 dB). This is why adding a second violin to an orchestra makes very little difference to overall volume — the orchestra's background noise dominates.
Hearing Damage and Safe Exposure
The Health and Safety Executive (UK) sets noise action levels: 80 dBA: employers must provide hearing protection if requested. 85 dBA: employers must supply and workers must use hearing protection. 87 dBA: absolute limit at ear (cannot be exceeded even with protection). Safe daily exposure times (approximately): 85 dB = 8 hours, 88 dB = 4 hours, 91 dB = 2 hours, 94 dB = 1 hour, 100 dB = 15 minutes, 110 dB = 2 minutes. Noise-induced hearing loss is permanent and cumulative — concert-going, power tools, and loud headphone use are among the most common everyday sources of preventable hearing damage.
Inverse Square Law
Sound intensity decreases with the square of distance: if you double your distance from a source, intensity reduces by 6 dB. At 1m from a speaker at 100 dB: at 2m = 94 dB, at 4m = 88 dB, at 10m = 80 dB, at 100m = 60 dB. This is why standing back from speakers at events reduces hearing damage risk dramatically. The inverse square law applies to point sources in open spaces — indoors, reflections mean sound does not decrease as rapidly with distance.
Common Sound Level Reference Chart
These are typical real-world sound levels — use them to sanity-check the result above against something you can actually picture.
| Level | Typical source |
|---|---|
| 0 dB | Threshold of human hearing |
| 10 dB | Breathing, rustling leaves |
| 30 dB | Quiet bedroom, whisper at 1m |
| 50 dB | Quiet office, moderate rainfall |
| 60 dB | Normal conversation at 1m |
| 70 dB | Busy traffic, vacuum cleaner |
| 80 dB | Alarm clock, HSE hearing-protection-if-requested level |
| 85 dB | Heavy traffic, HSE mandatory-hearing-protection level |
| 90 dB | Lawnmower, motorcycle at close range |
| 100 dB | Nightclub, power tools |
| 110 dB | Rock concert, chainsaw |
| 120 dB | Ambulance siren, thunderclap |
| 130+ dB | Threshold of pain, jet engine at takeoff |
Frequently Asked Questions
What is a decibel, in plain terms?
A decibel (dB) is a logarithmic unit for measuring sound intensity — logarithmic means every +10 dB represents roughly 10× more sound power, not 10× more "loudness" in a simple linear sense. This is why a jump from 60 dB (conversation) to 90 dB (lawnmower) feels far more than 1.5× louder — it's actually around 1,000× more sound power.
Why don't two 90 dB sounds combined equal 180 dB?
Because decibels are logarithmic, not linear — you can't add them directly. Two identical 90 dB sources together produce about 93 dB, not 180 dB. Use the "combine" mode above to calculate this properly for your own values; the reference chart below shows what different combined levels sound like in practice.
How much does sound level drop with distance?
Sound intensity follows the inverse square law: each time you double your distance from a source, the level drops by about 6 dB. Standing 4m from a 100 dB speaker instead of 1m away drops it to roughly 88 dB — enter your own source level and distances above to calculate this precisely.
What sound level is dangerous to my hearing?
In the UK, the Health and Safety Executive sets 80 dBA as the level where employers must provide hearing protection on request, 85 dBA as the level where protection becomes mandatory, and 87 dBA as an absolute limit that cannot be exceeded even with protection. Enter a sound level above to see its estimated safe daily exposure time.
How loud is a rock concert or nightclub compared to safe limits?
Rock concerts and nightclubs typically run 100-110+ dB — well above the 85 dB level where hearing protection becomes mandatory in occupational settings, and safe unprotected exposure time at that level is measured in minutes, not hours. See the reference chart below for how common everyday and loud environments compare.