Decibel Calculator
Combine sound levels in decibels or convert between a ratio and decibels. Decibels are logarithmic, so adding two equal sources raises the total by about 3 dB rather than doubling it.
How to use the decibel calculator
- To combine sources, enter one decibel level per line and read the total.
- To convert a ratio, switch modes and enter the ratio.
- Pick power or amplitude so the right 10x or 20x factor is used.
Examples
Two 80 dB sources
80, 80
83.01 dB
Power ratio of 2
ratio 2, power
3.01 dB
Frequently asked questions
How do you add decibels?
Convert each level back to a linear power with 10^(L/10), add them, then convert to decibels: 10 x log10(sum). You cannot simply add the dB numbers.
Why do two equal sources add only 3 dB?
Doubling power is a factor of 2, and 10 x log10(2) is about 3.01 dB. So two identical 80 dB sources together measure roughly 83 dB, not 160 dB.
What is the difference between power and amplitude decibels?
Power quantities use 10 x log10(ratio), while amplitude quantities such as voltage or sound pressure use 20 x log10(ratio), because power is proportional to amplitude squared.
How do I convert decibels back to a ratio?
Invert the formula: a power ratio is 10^(dB/10) and an amplitude ratio is 10^(dB/20). A 6 dB amplitude gain is a voltage ratio of about 2.
Does adding a much quieter source change the total?
Barely. Adding a source 10 dB lower raises the total by only about 0.4 dB, since the quieter source contributes a tenth of the power of the louder one.
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