Decibel Addition Calculator
Enter the sound level of each source in dB to find the combined level. This adds uncorrelated sources by their energy, which is how two 60 dB sources become about 63 dB.
What this calculation does
This tool adds the sound levels of uncorrelated sources by their energy (power). "Uncorrelated" means the phases of the sources are unrelated, so their energies simply add. This is the usual way to combine independent noise sources.
- Combined level (dB) = 10 × log10 (10^(L1 ÷ 10) + 10^(L2 ÷ 10) + …)
Decibels are a logarithmic scale, so levels cannot be added directly (60 + 60 is not 120). Each level is converted back to a power ratio, the ratios are added, and the sum is converted back to dB.
This is different from the Decibel Calculator, which converts a single ratio (such as a voltage ratio of 2) into decibels and back. This tool combines several levels into one.
Real sound levels can differ from this result
A real sound level can differ from this result because of phase and interference (sounds reinforcing or cancelling each other).
- Two loudspeakers playing the same signal can reinforce each other, giving more than the calculated level, or cancel each other, giving less, depending on position and frequency. When the signals are perfectly in phase, two equal sources add up to as much as 6 dB (uncorrelated sources add about 3 dB).
- So adding a second speaker does not always give the calculated result. Treat the result as an estimate.
- For speaker layout, design or any safety-related decision, check with actual measurements or dedicated simulation.
Examples
The examples show 2 decimal places. The tool shows 1 decimal place by default (63.0 dB for the first example); choose 2 above to see 63.01.
- 60 dB + 60 dB = about 63.01 dB (two equal sources add about 3 dB).
- 60 dB + 57 dB = about 61.76 dB.
- 60 dB + 50 dB = about 60.41 dB.
- 60 dB + 40 dB = about 60.04 dB (when the levels differ a lot, the quieter source barely matters).
When n sources have the same level
| Number of sources | Increase |
|---|---|
| 2 | +3.01 dB |
| 3 | +4.77 dB |
| 4 | +6.02 dB |
| 5 | +6.99 dB |
| 8 | +9.03 dB |
| 10 | +10.00 dB |
| 16 | +12.04 dB |
| 20 | +13.01 dB |
The increase is 10 × log10 (number of sources).
Two sources with different levels
The increase over the louder source depends on how many dB lower the quieter one is.
| Difference between the two | Increase over the louder one |
|---|---|
| 0 dB (equal) | +3.01 dB |
| 1 dB | +2.54 dB |
| 3 dB | +1.76 dB |
| 6 dB | +0.97 dB |
| 10 dB | +0.41 dB |
| 20 dB | +0.04 dB |
Notes
- Levels can be from −999 to 999 dB, with decimals, and negative values are allowed. You can use 2 to 20 sources (empty rows are ignored; with a single value, the result is that value).
- The result is rounded to 0, 1 or 2 decimal places (1 by default). Logarithms and powers are used, so ordinary floating-point arithmetic is involved.
- The levels are treated as plain dB values. Whether they are sound pressure levels at the same point, with the same weighting (such as dB(A)) and the same measurement conditions, is up to you.
- To convert a ratio to decibels or back, use the Decibel Calculator.
Frequently asked questions
What is 60 dB plus 60 dB?
About 63.01 dB, not 120 dB. Two equal uncorrelated sources add about 3 dB.
How many dB does doubling the number of sources add?
About 3.01 dB for uncorrelated sources. Ten times as many sources add 10 dB.
Do two identical speakers add 3 dB?
Not necessarily. Speakers playing the same signal can add up to 6 dB where they are in phase, and less where they cancel. This tool adds the energy of uncorrelated sources, so it does not describe two speakers playing the same signal exactly.
Can I add negative decibel values?
Yes. For example, −10 dB and −10 dB combine to about −6.99 dB.