Decibel Calculator
Add multiple sound levels in decibels the correct logarithmic way, and find how a level changes with distance from a point source. Runs entirely in your browser.
Combined level
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Level at d₂
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Show the math
Decibels are logarithmic, so levels don't simply add. Combine incoherent sources by summing their powers:
total = 10 × log₁₀(Σ 10^(Lₙ ÷ 10))
Two equal sources add about 3 dB, not double. For a point source, sound drops 6 dB each time the distance doubles:
L₂ = L₁ − 20 × log₁₀(d₂ ÷ d₁)
Everything is calculated in your browser.
What this does
A decibel calculator adds multiple sound levels the correct logarithmic way, and finds how a level changes with distance from a point source.
How to use it
- Enter each sound level in dB.
- Read the combined total.
- Or enter a level and two distances.
- Read the level at the new distance.
How it works
Decibels are logarithmic, so you sum the underlying powers — two equal sources add ~3 dB, not double. For a point source, level drops 6 dB each time distance doubles.
total = 10 × log₁₀(Σ 10^(Lₙ ÷ 10))
Understanding your result
The key insight is that decibels add logarithmically, not arithmetically, so two equal sources are about 3 dB louder, not twice as loud, and a quiet source barely changes a loud total. For distance, level drops about 6 dB each time you double the gap from a point source, which is why stepping back a little from a speaker cuts the level more than you would expect.
Example
Two 80 dB sources together reach about 83 dB.
Sources & methodology
Last updated .
Frequently asked questions
Why can’t I just add decibels?
Decibels are logarithmic, so you sum the underlying powers: total = 10 × log₁₀(Σ 10^(Lₙ ÷ 10)). Two equal sources add about 3 dB, not double.
How does distance change the level?
For a point source, sound drops 6 dB each time the distance doubles: L₂ = L₁ − 20 × log₁₀(d₂ ÷ d₁). Enter the level at one distance to find it at another.
Does this apply to every situation?
The distance formula assumes a free field and a point-like source. Indoors, reflections and reverberation reduce the drop-off, so treat it as a guide.
Do you store my numbers?
No. Everything is calculated locally in your browser.
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