Add multiple sound source dB values to calculate the combined total. Note: 80 dB + 80 dB ≈ 83 dB, not 160 dB.
A decibel (dB) is a logarithmic unit that expresses the ratio between two physical quantities. It is widely used in acoustics, audio engineering, and telecommunications. Rather than an absolute measurement, it represents how much a value differs from a reference on a log scale.
| dB | Power ratio | Amplitude ratio | Meaning |
|---|---|---|---|
| 0 dB | 1× | 1× | No change |
| 3 dB | 2× | 1.41× | Double power |
| 6 dB | 4× | 2× | Double amplitude |
| 10 dB | 10× | 3.16× | 10× power |
| 20 dB | 100× | 10× | 10× amplitude |
| −3 dB | 0.5× | 0.71× | Half power |
| −10 dB | 0.1× | 0.32× | 1/10 power |
| −20 dB | 0.01× | 0.1× | 1/10 amplitude |
| Level | Example |
|---|---|
| 0 dB | Threshold of hearing |
| 30 dB | Whisper, quiet bedroom |
| 60 dB | Normal conversation |
| 70 dB | Vacuum cleaner, busy street |
| 85 dB | Heavy traffic (hearing damage with prolonged exposure) |
| 100 dB | Chainsaw, motorcycle |
| 120 dB | Rock concert (threshold of pain) |
| 140 dB | Jet engine at takeoff (instant damage) |
A decibel is a logarithmic unit expressing the ratio between two physical quantities, used for sound pressure, power, and voltage. For power ratios, dB = 10×log10(P1/P2); for amplitude ratios, dB = 20×log10(A1/A2). Every 3 dB increase roughly doubles the power, and every 10 dB multiplies it by 10.
Sound levels cannot be added directly. Use the formula L_total = 10×log10(Σ 10^(Li/10)). For example, two 80 dB sources combine to about 83 dB, not 160 dB. The "Sound Level Sum" tab in this calculator handles this automatically.
Power ratios use a factor of 10: dB = 10×log10(P1/P2). Amplitude ratios (voltage, sound pressure) use a factor of 20: dB = 20×log10(A1/A2). This is because power is proportional to amplitude squared, and 10×log(x²) = 20×log(x).
Using dB = 10×log10(P1/P2), when P1/P2 = 2, dB = 10×log10(2) ≈ 3.01 dB. So doubling power adds about 3 dB, and halving it subtracts about 3 dB.
dBm is an absolute power unit referenced to 1 mW (0 dBm = 1 mW). dBW is referenced to 1 W (0 dBW = 1 W). dBA is an A-weighted sound pressure level approximating human hearing sensitivity. This calculator works with relative dB values.