Decibel Addition Calculator
Add sound levels the right way — combine up to four decibel sources on an energy basis to get the true total level for mixing and noise work.
How it works
L_total = 10 × log₁₀( Σ 10^(Lᵢ ÷ 10) ) · Two equal levels add +3.01 dB · Ten equal levels add +10 dB
Decibels are logarithmic, so you cannot simply add them — 80 dB plus 80 dB is not 160 dB. You convert each level back to a linear energy (power) with 10^(L/10), sum those, then convert the total back to decibels. Two equal sources add just over 3 dB because their energies double, and doubling on the log scale is +3.01 dB. This is why adding a second identical speaker or noise source barely moves the meter compared with what intuition suggests.
Worked example
Two 80 dB sources: each is 10^(80/10) = 10^8 in energy units, summing to 2 × 10^8. Convert back: 10 × log₁₀(2 × 10^8) = 83.01 dB. The pair is only about 3 dB louder than one alone — the classic +3 dB rule for doubling.
Frequently asked questions
Why does doubling a source add only 3 dB?
Sound level in decibels is ten times the log of power. Doubling the power (two identical sources) is 10 × log₁₀(2) ≈ 3.01 dB. It takes ten equal sources to add 10 dB, which is why crowd or machinery noise grows so slowly with more units.
Can I use this for uncorrelated noise?
Yes — this energy-summing method is exactly right for uncorrelated (incoherent) sources such as separate machines, instruments or noise sources. Perfectly correlated signals in phase would add differently, but that is rare outside a lab.
Why enter 0 to ignore a source?
A true 0 dB source is so quiet it barely affects the total, so the calculator treats 0 as "not used" and combines only the levels you enter above zero. Fill as many of the four fields as you need.
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This calculator is for educational purposes. Double-check important results before acting on them.