Decibel Addition Calculator

About this calculator

Because decibels are a logarithmic scale, two sound sources cannot simply be added arithmetically — a source at 70 dB next to another at 70 dB does not produce 140 dB. Instead, the combined level is L_total = 10·log₁₀(10^(L₁/10) + 10^(L₂/10)), which converts each level back to raw sound intensity, adds the intensities linearly, and converts the sum back to decibels. Two equal, incoherent sources combine to add about 3 dB to a single source's level, not double it.

Acoustic and noise-control engineers use this to predict the combined noise level of multiple machines, fans, or traffic lanes; audio engineers use it when summing microphone or speaker outputs; and occupational health and safety professionals use it to assess whether combined workplace noise exceeds exposure limits. Urban planners and environmental consultants also rely on it to model cumulative noise from combined sources like nearby roads or construction equipment.