How do you add decibels together?

Convert each level back to energy, add those, and convert back: 10 × log₁₀(Σ 10^(L/10)). Two equal sources always come out 3 dB above one of them, whatever the starting level.

Why is 3 dB a doubling of power but not of loudness?

3 dB is exactly twice the acoustic energy, but human hearing compresses that scale. Perceived loudness roughly doubles per 10 dB, so a 3 dB change is measurable, a 5 dB change is clearly audible, and a 10 dB change sounds twice as loud.

How much does sound level drop with distance?

6 dB per doubling of distance outdoors, because the energy spreads over the surface of an expanding sphere. A source measuring 100 dB at one metre reads 94 dB at two metres and 80 dB at ten.

How long can I safely be exposed to 95 dB?

Under the NIOSH criterion, about 47 minutes a day; under OSHA's more permissive rule, four hours. Hearing protection is recommended above 85 dB and effectively required near 100 dB.

How do I subtract background noise from a measurement?

Convert both readings to energy, subtract, and convert back. If the background is within 3 dB of the total the result is unreliable — the source is barely louder than the room.

Decibel Calculator

Add sound levels the way energy actually combines, work out how far a noise carries, and check the safe exposure time.

The Decibel Calculator runs entirely in your browser. Your measurements stay on your device.

Open the Wavelength & Frequency Calculator

关于 Decibel Calculator

Decibels are logarithmic, so the ordinary rules of addition do not apply: two 80 dB machines make 83 dB, not 160, and adding a 60 dB source to an 80 dB one changes almost nothing. Three facts do all the work here — equal sources add 3 dB, doubling the distance outdoors costs 6 dB, and it takes about 10 dB before a sound feels twice as loud, which is why a 3 dB rise doubles the measured energy while being barely noticeable to the ear. This calculator combines any number of sources, subtracts a background reading to isolate one, moves a measurement to a new distance, and converts a level into the daily exposure limits published by NIOSH and OSHA.

功能特性

Energy-correct addition of any number of sound levels
Background subtraction to isolate a single source
Level of N identical sources at once
Distance falloff at 6 dB per doubling, in either direction
Distance at which a source drops to a target level
NIOSH and OSHA daily exposure limits, which use different rules
Power and amplitude ratio conversions in both directions
A table of everyday sounds for context
Everything computes on your device

如何使用 Decibel Calculator

Choose whether you are adding sources, moving distance or checking exposure
Enter the measured levels in decibels
Read the combined level, the new level or the safe time
Compare against the everyday reference sounds

示例

输入

Two machines at 80 dB each

输出

83.01 dB combined — the second machine adds 3 dB
Safe NIOSH exposure at that level: 5.0 hours

Doubling the energy adds 3 dB; doubling the perceived loudness takes about 10.

常见错误与故障排除

Adding a quiet source changed nothing. — That is correct behaviour. A source 10 dB below another contributes about 0.4 dB, and one 20 dB below is effectively invisible — which is why quieting the loudest machine is the only change that matters.
The measured drop with distance is less than 6 dB per doubling. — Spherical spreading only applies outdoors with nothing to reflect off. Indoors, in a corridor or beside a wall, reflected energy keeps the level up, and a line of traffic behaves more like a line source at 3 dB per doubling.
NIOSH and OSHA give very different safe times. — They use different rules. NIOSH starts at 85 dB and halves the time every 3 dB; OSHA starts at 90 dB and halves every 5 dB. NIOSH is the more protective figure and the one hearing conservation programmes generally follow.

常见问题

How do you add decibels together?: Convert each level back to energy, add those, and convert back: 10 × log₁₀(Σ 10^(L/10)). Two equal sources always come out 3 dB above one of them, whatever the starting level.
Why is 3 dB a doubling of power but not of loudness?: 3 dB is exactly twice the acoustic energy, but human hearing compresses that scale. Perceived loudness roughly doubles per 10 dB, so a 3 dB change is measurable, a 5 dB change is clearly audible, and a 10 dB change sounds twice as loud.
How much does sound level drop with distance?: 6 dB per doubling of distance outdoors, because the energy spreads over the surface of an expanding sphere. A source measuring 100 dB at one metre reads 94 dB at two metres and 80 dB at ten.
How long can I safely be exposed to 95 dB?: Under the NIOSH criterion, about 47 minutes a day; under OSHA's more permissive rule, four hours. Hearing protection is recommended above 85 dB and effectively required near 100 dB.
How do I subtract background noise from a measurement?: Convert both readings to energy, subtract, and convert back. If the background is within 3 dB of the total the result is unreliable — the source is barely louder than the room.