A decibel calculator lets you add multiple sound sources correctly (logarithmically), convert dB levels to physical intensity, and check safe exposure times based on OSHA standards. Decibels are logarithmic — two 60 dB sources add up to ~63 dB, not 120 dB.
Combine Multiple Sound Sources
Add dB values from multiple sources to find the combined level.
dB to Intensity Converter
Common Sound Levels Reference
Safe Exposure Time Calculator
Based on OSHA 3 dB exchange rate (NIOSH recommends 3 dB, not the older 5 dB rate).
How to Use the Decibel Calculator
This calculator handles the three most common acoustic calculations: combining multiple sound sources, converting between dB and physical intensity, and checking whether a noise exposure level is safe for a given duration.
Combining Multiple Sources
Enter the dB level for each sound source in your environment. The tool applies the correct logarithmic addition formula: dB_total = 10 × log₁₀(Σ 10^(dBᵢ/10)). For example, a vacuum cleaner at 75 dB plus a dishwasher at 65 dB gives a combined level of 75.4 dB — barely more than the louder source alone.
Understanding dB Addition
Adding two identical sources increases the total by exactly 3 dB. Two 70 dB sources = 73 dB total. Ten 70 dB sources = 80 dB. This is because dB is logarithmic: doubling the power adds 3 dB, multiplying power by 10 adds 10 dB. This is why a concert venue needs hundreds of speakers to meaningfully increase volume beyond a single stack.
dB to Intensity Conversion
Sound intensity in W/m² follows I = I₀ × 10^(dB/10), where I₀ = 10⁻¹² W/m². Normal conversation at 60 dB corresponds to 10⁻⁶ W/m² (one microwatt per square meter). A rock concert at 110 dB reaches 0.1 W/m² — ten million times more intense than a whisper at 20 dB.
Safe Exposure Times
The OSHA and NIOSH 3 dB exchange rate means the safe exposure time halves for each 3 dB increase above 85 dB: 85 dB = 8 hours, 88 dB = 4 hours, 91 dB = 2 hours, 94 dB = 1 hour, 100 dB = 15 minutes, 110 dB = about 1 minute. Exposure above 140 dB — even briefly — can cause immediate permanent hearing damage.
FAQ
Can you just add decibel levels from two sources?
No — decibels are logarithmic. Two sources at 60 dB each do NOT produce 120 dB. The correct formula is dB_total = 10 × log10(10^(dB1/10) + 10^(dB2/10)). Two identical 60 dB sources produce about 63 dB — only a 3 dB increase. To double perceived loudness requires about a 10 dB increase.
What is the reference intensity for sound?
The standard reference intensity is I₀ = 10⁻¹² W/m² — the threshold of human hearing at 1 kHz. The decibel scale then maps 0 dB (threshold) to about 120 dB (pain threshold) and 194 dB (theoretical maximum in air). To convert: I = I₀ × 10^(dB/10).
At what dB level does hearing damage occur?
The OSHA 3 dB exchange rate: damage begins with prolonged exposure above 85 dB. At 85 dB, the safe limit is 8 hours. Each additional 3 dB halves the safe exposure time — so 91 dB allows only 2 hours, and 100 dB allows only 15 minutes.
Is this tool free?
Yes, completely free with no signup required. All calculations run in your browser.
Is my data private?
Yes. All calculations run locally. No data is sent to any server.
Why does 10 dB sound twice as loud?
Human perception of loudness (measured in sones) roughly doubles with every 10 dB increase. The intensity increases by 10x with each 10 dB, but our perception is logarithmic too. A 3 dB increase roughly doubles the physical power, while a 10 dB increase makes it sound about twice as loud.
What is 0 dB — is it silence?
0 dB SPL is the threshold of human hearing (I₀ = 10⁻¹² W/m²), not absolute silence. Negative dB values are below the threshold of normal hearing. A perfectly quiet anechoic chamber measures around -9 dB SPL — the quietest place on Earth.