Introduction
Sound level is measured in decibels (dB) — a logarithmic ratio. 0 dB is the threshold of human hearing; 60 dB is normal conversation; 85 dB is hazardous with prolonged exposure; 120 dB is a rock concert; 140 dB is a jet engine at 25 m. The logarithmic scale means +10 dB is ten times more energy (and perceived roughly twice as loud). This calculator is mostly placeholder — decibels don't convert to a linear unit; they are a unit.
Why sound level units exist and how they diverged
The decibel is not a unit in the usual sense — it's a logarithmic ratio. dB SPL (sound pressure level) references 20 µPa (the threshold of human hearing); dB HL (hearing level) references the normal-young-adult audiogram; dB A (A-weighted) approximates human frequency sensitivity. Different weightings matter: a 100 dB SPL bass tone is perceived quieter than a 100 dB SPL midrange tone.
How to convert sound level
dB change: +3 dB = 2× the power; +10 dB = 10× the power; +20 dB = 100×. Human perception: +10 dB is roughly 'twice as loud' subjectively. Safe exposure (OSHA): 85 dB for 8 hours, 88 dB for 4 hours, halving allowed time per 3 dB increase.
Units supported by this sound level calculator
- Decibel (dB)
- Bel (B)
- Neper (Np)
- Centibel (cdB)
- Phon (~ dB at 1 kHz)
- dB(A)
- dB(C)
- Sone (approx, 1 sone ≈ 40 phon)
Common sound level conversion mistakes
- Adding decibels naively. Two 50 dB sources aren't 100 dB — they're 53 dB (3 dB for doubling power). You can't add decibels arithmetically.
- dBA vs dB SPL vs dB HL. Different references. A sound level meter set to dBA weights human-audible frequencies.
- Peak vs RMS. Impulse noise (gunshot) has a high peak dB but brief duration — the damage profile differs from sustained noise.
- Hearing protection ratings. A '30 dB' NRR earplug reduces real exposure by only ~15-20 dB in practice (imperfect fit).
Real-world sound level examples
- Threshold of hearing: 0 dB SPL.
- Whisper at 1 m: 30 dB.
- Normal conversation: 60 dB.
- Busy restaurant: 70 dB.
- Vacuum cleaner: 70-75 dB.
- City traffic: 75-85 dB.
- Lawnmower: 90 dB.
- Rock concert: 110-120 dB.
- Jet takeoff (25 m away): 140 dB (pain threshold).
- Firearm (at the shooter's ear): 160 dB unprotected — instant hearing damage.
Tips for accurate sound level conversion
- Anything above 85 dB with prolonged exposure damages hearing. Use ear protection for concerts, power tools, firearms.
- For baby safety, keep nursery below 50 dB.
- Sleep is disturbed above 40 dB — why urban bedrooms benefit from soundproofing.
Related: Frequency Converter · Power Converter · SI Prefix Converter.