Sound Level Addition Calculator
Add multiple decibel sound levels correctly using logarithmic combination.
Calculate combined SPL from two or more noise sources.
Convert between dB and sound intensity or pressure.
Why You Can’t Just Add Decibels Decibels are on a logarithmic scale: 60 dB + 60 dB ≠ 120 dB. Two equal sound sources add only 3 dB (not double) because intensity doubles. 60 dB + 60 dB = 63 dB. 70 dB + 60 dB ≈ 70.4 dB (louder one dominates).
Combining Sound Levels L_total = 10 × log₁₀(10^(L₁/10) + 10^(L₂/10) + … + 10^(Lₙ/10)) This converts each source back to intensity (relative), sums them, then converts back to dB.
Quick Rules Same level, 2 sources: L_total = L + 3 dB Same level, 4 sources: L_total = L + 6 dB Same level, 10 sources: L_total = L + 10 dB Difference ≥ 10 dB: louder source dominates (+ 0.4 dB or less) Difference 5 dB: combined = louder + 1.2 dB Difference 3 dB: combined = louder + 1.8 dB Difference 0 dB: combined = louder + 3 dB
dB Reference Values dB SPL (sound pressure level): reference 20 μPa (threshold of hearing) dB SIL (intensity): reference 10⁻¹² W/m² L_p = 20 × log₁₀(p / p_ref) — pressure ratio L_I = 10 × log₁₀(I / I_ref) — intensity ratio
Common Sound Levels (dB SPL) Threshold of hearing: 0 dB | Whisper: 30 dB Conversation: 60 dB | Traffic: 70 dB Lawnmower: 90 dB | Concert: 110 dB Jet takeoff: 130 dB | Pain threshold: 140 dB