Decibel Calculator
Combine several sound levels into one total, or convert between a linear ratio and decibels in either direction. Because decibels are logarithmic, the tool sums the underlying powers rather than the dB numbers, so two equal sources add about 3 dB instead of doubling. Switch between the power and amplitude scales so the correct 10x or 20x factor is applied.
How to use the decibel calculator
- Choose a mode at the top: Add levels, Ratio to dB, or dB to ratio.
- In Add levels, type one decibel level per line (commas and spaces also separate values) to get the combined total.
- In Ratio to dB, enter a linear ratio and pick Power or Amplitude.
- In dB to ratio, enter a decibel value and pick Power or Amplitude.
- Read the highlighted result and click Copy to save it.
Examples
Two 80 dB sources combined
80, 80
83.0103 dB
Power ratio of 2 to dB
ratio 2, power
3.0103 dB
6 dB amplitude gain back to a ratio
6 dB, amplitude
1.995262
Frequently asked questions
How do you add decibels?
Convert each level back to a linear power with 10^(L/10), add those powers, then convert to decibels with 10 times log10 of the sum. You cannot simply add the dB numbers because the scale is logarithmic.
Why do two equal sources add only about 3 dB?
Doubling the power is a factor of 2, and 10 times log10 of 2 is about 3.01 dB. So two identical 80 dB sources together measure 83.0103 dB, not 160 dB.
What is the difference between power and amplitude decibels?
Power quantities use 10 times log10 of the ratio, while amplitude quantities such as voltage, current or sound pressure use 20 times log10, because power is proportional to amplitude squared. The Power and Amplitude selector picks the right factor.
How do I convert decibels back to a ratio?
Invert the formula: a power ratio is 10^(dB/10) and an amplitude ratio is 10^(dB/20). A 6 dB amplitude gain works out to a voltage ratio of about 1.995262, which is close to 2.
Why does 6 dB double amplitude but only 3 dB doubles power?
Doubling power adds 10 times log10 of 2, about 3 dB. Doubling amplitude adds 20 times log10 of 2, about 6 dB, because on the amplitude scale the multiplier is 20 rather than 10.
Does adding a much quieter source change the total?
Barely. Adding a source 10 dB lower raises the total by only about 0.4 dB, for example 80 dB plus 70 dB gives 80.413927 dB, because the quieter source carries a tenth of the louder one's power.
How do I enter multiple levels?
In Add levels type one number per line, or separate them with commas or spaces. Every value is treated as a level in decibels, and blank lines are ignored.
Can I use negative decibels or a ratio below one?
Yes for decibels; a negative dB simply means a level below the reference. In the Ratio to dB mode the ratio must be greater than zero, and a ratio between 0 and 1 gives a negative dB, marking attenuation rather than gain.
Is this the same as a loudness or dBA reading?
No. The tool does the exact logarithmic math on the numbers you supply. It does not apply A-weighting or model how loud a sound feels, so feed it measured sound pressure levels if you want a physical total.
Does anything get uploaded?
No. The calculation runs entirely in your browser, so the levels and ratios you enter never leave your device.
Learn more
- The decibel scale: why 3 dB and 6 dB matter
How the logarithmic decibel scale works, why 3 dB doubles power and 6 dB doubles amplitude, and how to combine noise sources.
Related tools
Note Frequency Calculator
Convert any musical note to its frequency in Hz, or a frequency back to the nearest note and cents. Equal temperament with an adjustable A4 tuning.
Wavelength Frequency Calculator
Convert wavelength to frequency and back using c = f x lambda. Enter a wavelength or frequency in metres, nm, Hz, MHz or GHz and get the photon energy too.
555 Timer Calculator
Calculate 555 timer astable frequency, period, high and low times and duty cycle from R1, R2 and the timing capacitor. Free oscillator design helper.
Absolute Humidity Calculator
Calculate absolute humidity in grams of water vapor per cubic meter from air temperature and relative humidity. Fast, free and works in your browser.
Allele Frequency Calculator
Find allele frequencies from genotype counts. Enter the number of AA, Aa and aa individuals to get the A and a allele frequencies and allele totals.
Angular Acceleration Calculator
Find angular acceleration from a change in angular velocity over time, and the torque from a moment of inertia. Enter start and end rad/s and the time.