Quick answer
Sound levels combine logarithmically: L_total = 10 log₁₀ Σ 10^(Lᵢ ÷ 10). Two sources of 60 dB together give 63.01 dB, not 120.
Choose a mode and enter the levels to combine, or an intensity. The calculator returns the combined level.
Related tools: Doppler Effect Calculator: Observed frequency from source and observer speeds. Dew Point Calculator: Dew point from temperature and relative humidity. Acceleration Calculator: Average acceleration from change in velocity over time.
How to use the Sound Level Calculator
- Choose use: Combine several levels (dB) and Intensity → dB.
- Optionally, type levels to combine (dB), for example 85, 80, 75.
- Optionally, enter sound intensity (W/m²) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Use | Choose one: Combine several levels (dB); Intensity → dB | Starts at Combine several levels (dB) |
| Levels to combine (dB) (optional) | Text, such as 85, 80, 75 | — |
| Sound intensity (optional) | A number, in W/m² | > 0 |
Formula and method
Formula
L = 10 log₁₀(I ÷ 10⁻¹² W/m²); L_total = 10 log₁₀ Σ 10^(Lᵢ ÷ 10)
IEEE-754 double precision; shown to the decimals indicated.
Reference intensity 10⁻¹² W/m². Levels add on an energy basis, not arithmetically.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Use = Combine several levels (dB); Levels to combine (dB) = 60, 60.
| Result | Value |
|---|---|
| Combined level | 63.01 dB |
Example 2
Inputs: Use = Combine several levels (dB); Levels to combine (dB) = 85, 80, 75.
| Result | Value |
|---|---|
| Combined level | 86.51 dB |
Example 3
Inputs: Use = Combine several levels (dB); Levels to combine (dB) = 50.
| Result | Value |
|---|---|
| Combined level | 50 dB |
The first line is the headline result (combined level). IEEE-754 double precision; shown to the decimals indicated.
Why +3 dB
Doubling the sound power adds 10 log₁₀ 2 = 3.01 dB. So two identical sources are 3 dB louder, and ten identical sources 10 dB louder.
Perceived loudness
A 10 dB increase is perceived as roughly twice as loud. 85 dB is the level at which prolonged exposure risks hearing damage. The calculator assumes incoherent sources (no interference).
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Levels to combine (dB): left empty shows "Enter at least one number." beside that field and no result.
- Sound intensity: left empty shows "Enter the sound intensity." beside that field and no result.
Choosing between the Sound Level Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Doppler Effect Calculator](/science/doppler-effect-calculator/) | source frequency, source speed toward the observer and observer speed toward the source | Observed frequency |
| [Dew Point Calculator](/science/dew-point/) | air temperature and relative humidity | Dew point |
| [Acceleration Calculator](/science/acceleration-calculator/) | initial velocity, final velocity and time | Acceleration |
| [Mole Calculator](/science/mole/) | start from and molar mass | Amount |
| [Density Calculator](/science/density-calculator/) | Mass |
Background: environment and acoustics
Decibels are a logarithmic scale, so sound levels cannot be added arithmetically: two equal sources raise the level by about 3 dB, not double it. Environmental and emissions results depend on the factors behind them (for example the US EPA's equivalency factors), which are averages for a country, fuel and year.
Use the result to compare scenarios rather than as a measured value.
Assumptions and limitations
- Incoherent sources only
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for levels to combine (dB) and sound intensity to confirm this.
Frequently asked questions
What is 70 dB plus 70 dB?
Two equal sources add 3 dB: 70 dB + 70 dB = 73 dB, not 140.
What is 60 dB plus 50 dB?
60 dB + 50 dB = 10·log₁₀(10⁶ + 10⁵) ≈ 60.4 dB; the quieter source adds little.
What is the threshold of hearing?
The threshold of hearing is defined as 0 dB, which equals an intensity of 10⁻¹² W/m².
What does the Sound Level Calculator calculate?
Combine decibel levels, or convert sound intensity to decibels. It returns Combined level.
What formula does the Sound Level Calculator use?
L = 10 log₁₀(I ÷ 10⁻¹² W/m²); L_total = 10 log₁₀ Σ 10^(Lᵢ ÷ 10). Reference intensity 10⁻¹² W/m².
What do I need to enter in the sound Level Calculator?
You enter Use. Optional: Levels to combine (dB) and Sound intensity (W/m²).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Incoherent sources only.
What does the “Use” option change?
It sets how the sound Level is worked out. The choices are Combine several levels (dB) and Intensity → dB.
What is an example of a sound Level result?
With use Combine several levels (dB) and levels to combine (dB) 60, 60, the combined level is 63.01 dB.
Where does the method come from?
The method follows: Standard acoustics definition (ISO 80000-8).
Related calculators
- Doppler Effect Calculator — Observed frequency from source and observer speeds.
- Dew Point Calculator — Dew point from temperature and relative humidity.
- Acceleration Calculator — Average acceleration from change in velocity over time.
- Mole Calculator — Convert between mass, moles and number of particles.
- Density Calculator — Solve mass, density or volume.
- Half-Life Calculator — Remaining amount, elapsed time or half-life from exponential decay.
Sources
- Standard acoustics definition (ISO 80000-8)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.