Decibel Calculator
Add sound levels correctly in decibels, convert between dB and ratio, and see how distance attenuates a sound source.
Result (dB)
71.19
Breakdown
- Gain over the louder source (dB)
- 1.19
- dB of a 2× ratio (reference)
- 3.01
- Metres to fade to 0 dB SPL (free field)
- 3,627.99
Last updated:
FAQ
How do you add decibels correctly?
Decibels are logarithmic, so two 70 dB machines don't make 140 dB — energies add linearly. 70 dB + 70 dB = 73 dB, and 70 dB + 65 dB = 71.2 dB. Two equal sources gain just 3 dB; ten equal sources gain 10 dB.
Why is 3 dB the doubling rule?
Because 10·log₁₀(2) = 3.01: doubling acoustic power raises the level by about 3 dB, which is only barely audible. Perceived loudness roughly doubles every +10 dB — a tenfold power increase.
How quickly does sound fade with distance?
In a free field, sound pressure falls with the inverse of distance — 6 dB per doubling. The 'fade to 0 dB' figure assumes that ideal falloff with no walls, wind, or ground absorption; indoors, reflections slow the decay.
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