Amplifier Power and SPL Calculator
Calculate SPL at any distance from amp power and speaker sensitivity.
Convert between watts and dBW and check hearing safety limits for any setup.
Speaker Sensitivity Speaker sensitivity is measured as dB SPL at 1 meter with 1 watt (1W/1m). Typical home speakers: 85–92 dB/W/m. PA speakers / line arrays: 95–105 dB/W/m. High-efficiency horn speakers: 103–110 dB/W/m. Higher sensitivity = louder with same amplifier power.
SPL from Power and Distance SPL at 1m = Sensitivity + 10 × log₁₀(Power in watts) SPL at distance d = SPL at 1m − 20 × log₁₀(d) The −20 dB/decade drop is the inverse square law for spherical radiation. A doubling of distance reduces SPL by ~6 dB; halving distance adds ~6 dB.
Doubling Power Every doubling of amplifier power adds +3 dB SPL. 10× power = +10 dB (sounds about twice as loud to human hearing). 100× power = +20 dB (sounds about 4× as loud). This is why going from 100W to 200W is barely noticeable (+3 dB).
Adding More Speakers N identical boxes, each fed the same power: SPL increase = 10 × log₁₀(N) 2 speakers: +3 dB | 4 speakers: +6 dB | 8 speakers: +9 dB
This is the power sum, and it is the figure to plan with. You will also see +6 dB per doubling quoted, and that is not a mistake either: it is what you get when two sources are genuinely coherent at the listening position, meaning their pressures add rather than their powers. Real boxes playing real music only manage that at low frequencies, where the wavelength is long enough that the two arrivals stay in step. Higher up, the path lengths differ by more than half a wavelength and the sum wanders between +6 and cancellation depending on where you stand and what note is playing. Averaged across the spectrum and across the room it lands on +3, which is why +3 is the number the trade uses.
Hearing Safety NIOSH sets 85 dB for 8 hours and halves the allowance for every 3 dB on top, which is one formula rather than a table to memorize:
Allowed time (hours) = 8 × 2^((85 − Level) / 3)
85 dB = 8 hours | 88 dB = 4 hours | 91 dB = 2 hours | 94 dB = 1 hour 100 dB = 15 minutes | 110 dB = 1.5 minutes | 120 dB = 9 seconds
The 3 dB step is the part worth internalizing. Three decibels sounds like almost nothing, and it costs you half your day.
Reference: 0 dB SPL ≈ threshold of hearing; 194 dB = pressure of 1 atmosphere (theoretical max)
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