How do you average decibels?

Noise levels are averaged by energy (power average), not by adding the values and dividing: 10 × log10((10^(L1/10) + 10^(L2/10) + …) ÷ n). The arithmetic mean of 60, 70 and 80 dB is 70 dB, but the energy average is about 75.7 dB, because louder sounds count for more.

How do you correct for background noise?

If the level is 65 dB with the source on and 60 dB with it off (background noise), the source alone is 10 × log10(10^6.5 − 10^6) ≈ 63.3 dB. With the JIS Z 8731 correction, the difference is 5 dB, so you subtract 2 dB and get 63 dB. With a difference of 10 dB or more there is no correction; below 3 dB you measure again.

How much does noise drop when the distance doubles?

About 6 dB for a point source such as an outdoor unit or machine, and about 3 dB for a line source such as a busy road. A point source of 80 dB at 1 m is 60 dB at 10 m, and falls to 45 dB about 56 m away (a rough guide for open ground with no obstacles).

How many times louder is 10 dB more?

The sound energy (intensity) is 10 times, the sound pressure about 3.16 times, and it sounds roughly twice as loud. 20 dB is 100 times the energy and 10 times the pressure, and 3 dB is about twice the energy.

How many dB is a sound pressure of 1 Pa?

About 94 dB. Sound pressure level is 20 × log10(pressure ÷ 20 µPa), and 20 µPa (0.00002 Pa) is 0 dB. Sound level meters are often calibrated at 94 dB (1 Pa) or 114 dB (10 Pa).

Decibel Calculator | Adding Noise Levels in dB, Energy Average and n Identical Sources, Subtracting Background Noise (JIS Z 8731 Correction), Distance Attenuation for Point and Line Sources, Sound Pressure Pa to dB, How Many Times Louder a dB Difference Is, dB Addition Chart, Typical Noise Levels and Environmental Quality Standards

The Decibel Calculator handles noise level (dB) calculations that cannot be done with plain arithmetic, such as “what is 60 dB plus 60 dB?”, “how loud is an air conditioner's outdoor unit 10 m away?” and “how loud is the source once the background noise is removed?”. In the addition tab, list your measured values to get the combined level, worked out by converting each value back to sound energy 10^(L/10), and the energy average used for noise (with the difference from the arithmetic mean); it also gives L + 10 × log10(n) for n sources of the same level. In the subtraction tab, enter the level with the source on and off (background noise) to get the level of the source alone, together with the JIS Z 8731 correction (−3 for a 3 dB difference, −2 for 4–5 dB, −1 for 6–9 dB, none from 10 dB). In the distance attenuation tab, choose a point source (about −6 dB per doubling of distance) or a line source (about −3 dB) to get the level at the distance you want, the distance at which the noise falls to a target level, and a chart by distance. It also converts sound pressure in Pa to dB, shows how many times stronger a dB difference is in energy, sound pressure and perceived loudness, and includes a dB addition chart, typical noise levels such as a library at 40 dB and normal conversation at 60 dB, and Japan's environmental quality standards for noise (day and night).

Adding dB (combined level) and energy average

Get the level of several sounds playing at once and the average of measured values. Decibels cannot be added directly, so they are converted back to sound energy first.

Sound levels (dB), one per line or separated by commas

Combined level (sum)

71.5 dB

3 sounds

Above the loudest sound

+1.5 dB

Loudest 70.0 dB

Energy average

66.7 dB

Use this to average noise

Arithmetic mean (for reference)

65.0 dB

The values added and divided as they are

Formula: 10 × log10(10^(L1/10) + 10^(L2/10) + …). Two sounds of the same level add 3 dB; a sound 10 dB or more quieter hardly changes the total (+0.4 dB or less).

Several sounds of the same level

The level when you run several identical machines, or when the same sound comes from several people at once.

Level of one sounddBNumbersources

Combined level

63.0 dB

+3.0 dB over one (10 × log10(2))

Enter values measured with A-weighting (dB(A)). Smartphone sound level meter apps can be a few dB off depending on the model, so for complaints or official reports, measure with a calibrated sound level meter.

ABOUT

About Decibel Calculator | Adding Noise Levels in dB, Energy Average and n Identical Sources, Subtracting Background Noise (JIS Z 8731 Correction), Distance Attenuation for Point and Line Sources, Sound Pressure Pa to dB, How Many Times Louder a dB Difference Is, dB Addition Chart, Typical Noise Levels and Environmental Quality Standards

The Decibel Calculator adds noise levels in dB, takes their energy average, subtracts background noise and works out distance attenuation for point and line sources. It also converts sound pressure in Pa to dB, shows how many times louder a dB difference is, and includes a dB addition chart, typical noise levels and environmental standards.

How to use Decibel Calculator | Adding Noise Levels in dB, Energy Average and n Identical Sources, Subtracting Background Noise (JIS Z 8731 Correction), Distance Attenuation for Point and Line Sources, Sound Pressure Pa to dB, How Many Times Louder a dB Difference Is, dB Addition Chart, Typical Noise Levels and Environmental Quality Standards

1In “Add & average”, enter the measured dB values, one per line or separated by commas
2Check the combined level and the energy average. For several sources of the same level, enter the level of one and the number of sources
3In “Subtract (background noise)”, enter the level with the source on and off, and check the level of the source alone and the JIS correction
4In “Distance attenuation”, choose a point or line source and enter the measured level and distance, the distance you want and a target level
5In “Conversions & charts”, check the Pa to dB conversion, the ratio for a dB difference, typical noise levels and environmental standards

Great for

Estimating the noise of two or three air conditioner outdoor units or machines side by side
Averaging several noise measurements correctly (by energy)
Removing the surrounding (background) noise from a sound level meter reading to get the level of the source
Finding how loud construction work or an outdoor unit will be at a neighbour's house a few metres away
Finding how far from the source the noise falls to a level such as the 45 dB environmental standard
Comparing a noise level with a library, normal conversation and other everyday sounds

Good to know

Decibels are logarithmic, so they cannot be added or averaged directly. The tool converts them back to 10^(L/10) (sound energy), calculates, and converts back to dB with 10 × log10.
The background noise correction is 10 × log10(10^(total/10) − 10^(background/10)). The JIS Z 8731 correction is −3 for a 3 dB difference, −2 for 4–5 dB, −1 for 6–9 dB and none from 10 dB; below 3 dB you need to measure again.
Distance attenuation is L1 − 20 × log10(r2 ÷ r1) for a point source (about −6 dB per doubling) and L1 − 10 × log10(r2 ÷ r1) for a line source (about −3 dB). Walls, buildings, the ground and air absorption are not included, so the real level is often a little lower.
The typical noise levels are commonly used examples and change with distance and measuring method. The environmental standards are Japan's Environmental Quality Standards for Noise; the area categories are designated by prefectures and cities.
Smartphone sound level meter apps can be a few dB off depending on the model. For complaints or official reports, measure with a calibrated sound level meter (A-weighted).

Questions this tool answers

Use Decibel Calculator | Adding Noise Levels in dB, Energy Average and n Identical Sources, Subtracting Background Noise (JIS Z 8731 Correction), Distance Attenuation for Point and Line Sources, Sound Pressure Pa to dB, How Many Times Louder a dB Difference Is, dB Addition Chart, Typical Noise Levels and Environmental Quality Standards for searches like these:

Add decibels
Find the combined level of several noises
Calculate a background noise correction
Calculate noise distance attenuation
Average dB values correctly
Find how many dB a noise is a given distance away

FAQ

What is 60 dB plus 60 dB?: 63 dB (not 120 dB). Two sources of the same level add 3 dB, four add 6 dB and ten add 10 dB. For 60, 65 and 70 dB, the total is about 71.5 dB, only 1.5 dB more than the loudest, 70 dB.
How do you average decibels?: Noise levels are averaged by energy (power average), not by adding the values and dividing: 10 × log10((10^(L1/10) + 10^(L2/10) + …) ÷ n). The arithmetic mean of 60, 70 and 80 dB is 70 dB, but the energy average is about 75.7 dB, because louder sounds count for more.
How do you correct for background noise?: If the level is 65 dB with the source on and 60 dB with it off (background noise), the source alone is 10 × log10(10^6.5 − 10^6) ≈ 63.3 dB. With the JIS Z 8731 correction, the difference is 5 dB, so you subtract 2 dB and get 63 dB. With a difference of 10 dB or more there is no correction; below 3 dB you measure again.
How much does noise drop when the distance doubles?: About 6 dB for a point source such as an outdoor unit or machine, and about 3 dB for a line source such as a busy road. A point source of 80 dB at 1 m is 60 dB at 10 m, and falls to 45 dB about 56 m away (a rough guide for open ground with no obstacles).
How many times louder is 10 dB more?: The sound energy (intensity) is 10 times, the sound pressure about 3.16 times, and it sounds roughly twice as loud. 20 dB is 100 times the energy and 10 times the pressure, and 3 dB is about twice the energy.
How many dB is a sound pressure of 1 Pa?: About 94 dB. Sound pressure level is 20 × log10(pressure ÷ 20 µPa), and 20 µPa (0.00002 Pa) is 0 dB. Sound level meters are often calibrated at 94 dB (1 Pa) or 114 dB (10 Pa).

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