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About this tool
Turn a decibel change into amplitude, power and perceived-loudness ratios, plus the equivalent distance and source count.
A decibel change calculator converts a level difference in dB into the ratios it actually represents: power ratio 10^(dB/10), amplitude or sound-pressure ratio 10^(dB/20), and perceived loudness 2^(dB/10). It also gives the two practical equivalents — the distance ratio 10^(−dB/20) from the inverse-square law, and the number of identical uncorrelated sources that would produce the same rise. It is for audio engineers, acoustics students and anyone deciding whether a +3 dB change is worth chasing.
Open Decibel Change Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Power uses 10·log₁₀ and amplitude uses 20·log₁₀ — the tool shows both ratios for the same dB figure, so the factor of two is never guessed.
The sone-based +10 dB ≈ twice as loud rule is applied separately, because the ear does not follow either the power or amplitude ratio.
Every level change is also expressed as a distance ratio and a count of identical uncorrelated sources — the two things that change level on a real site.
3 dB is exactly double the power (3.01 dB, since 10·log₁₀2 = 3.0103) but only 1.41 times the amplitude, and the ear hears it as about 1.23 times as loud. It is a clearly audible step in an A/B comparison, and nowhere near twice as loud.
Because power is proportional to the square of a field quantity such as sound pressure or voltage. Decibels for power are 10·log₁₀(ratio) and for amplitude 20·log₁₀(ratio), so doubling the amplitude quadruples the power — 20·log₁₀2 = 6.02 dB against 10·log₁₀2 = 3.01 dB.
About 10 dB. On Stevens' sone scale, used in ISO 532 loudness standards, a 10 dB rise is heard as roughly a doubling of loudness for steady broadband sound well above threshold — even though 10 dB is ten times the power and only 3.16 times the sound pressure.
About 6.02 dB for every doubling of distance from a point source in free field, which is the inverse-square law written as 20·log₁₀2. So 2 metres to 8 metres is two doublings, or about 12 dB. Indoors the drop is smaller because reflected sound fills in the difference, and a line source such as a busy road falls at roughly 3 dB per doubling instead.
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