How do you add noise levels in dB?

Decibels are added logarithmically: L_total = 10 × log10(10^(L1/10) + 10^(L2/10) + ...). You cannot simply add dB values arithmetically.

What happens when you add two equal noise sources?

Two equal sources add 3 dB. For example, two 80 dB sources produce 83 dB combined. This is because 10×log10(2) ≈ 3.01.

Does a quiet source matter next to a loud one?

If the difference is >10 dB, the quieter source adds less than 0.4 dB. At >15 dB difference, the contribution is negligible (<0.1 dB).

What is the difference between dB and dBA?

dBA applies A-weighting that filters frequencies similar to human hearing. Low and very high frequencies are attenuated. dBA is used for most occupational noise measurements.

What is the occupational noise exposure limit?

Most standards set 85 dBA as the 8-hour exposure limit (e.g., OSHA, EU Directive 2003/10/EC). Above this level, hearing protection is mandatory.

Free Engineering Tool #214

Noise Level Addition Calculator

Combine up to 8 noise sources using logarithmic dB addition. Enter each source level in dB or dBA.

L = 10·log₁₀(Σ10^(Li/10))Up to 8 SourcesdB / dBA

Results

Combined Noise Level

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Number of Sources

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Increase over Loudest

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Noise Sources Bar Chart

Logarithmic dB Addition

Adding two equal sources increases level by 3 dB
If difference >10 dB, the quieter source contributes <0.4 dB
Adding 10 equal sources increases level by 10 dB

Example — 85 + 82 + 78 dB

L = 10×log10(10^8.5 + 10^8.2 + 10^7.8) = 10×log10(3.16×10⁸ + 1.58×10⁸ + 0.63×10⁸)

= 10×log10(5.37×10⁸) = 87.3 dB

Noise Level Addition Calculator | Combine dB Sources | Free Tool

Published by Nikolai Shelkovenko on February 15, 2026 February 15, 2026

Results

Logarithmic dB Addition