Loudspeaker SPL at Distance Calculator
A loudspeaker's sensitivity rating tells you how loud it is at 1 metre on 1 watt. To find the level at a real listening distance with a real amplifier, you add the gain from amplifier power and subtract the inverse-square distance loss. This calculator does both. Enter the speaker sensitivity, the amplifier power driving it, and the listening distance to get the expected sound pressure level, along with the separate power gain and distance loss terms. The figure is the on-axis free-field level and does not include room reverberation or boundary reinforcement.
SPL at distance formula
Power gain = 10 * log10(power in watts)
Distance loss = 20 * log10(distance in metres)
SPL = sensitivity + power gain - distance loss
Sensitivity is referenced to 1 watt at 1 metre, so the power gain is zero at 1 watt and the distance loss is zero at 1 metre. Each tenfold rise in power adds 10 decibels; each doubling of distance subtracts about 6 decibels.
Worked example
A 90 dB speaker on 100 watts at 4 metres: power gain = 10 * log10(100) = 20 dB, distance loss = 20 * log10(4) = 12.04 dB. SPL = 90 + 20 - 12.04 = 97.96 dB.
Loudspeaker SPL: frequently asked questions
What is loudspeaker sensitivity?
Sensitivity is the sound pressure level a loudspeaker produces at 1 metre when driven with a reference input, conventionally 1 watt into the rated impedance (often written as 1 W / 1 m). A speaker rated 88 dB is quieter for a given input than one rated 96 dB. Sensitivity is the starting point for predicting real-world levels.
What is the SPL at distance formula?
SPL = sensitivity + 10 times log10(power in watts) minus 20 times log10(distance in metres). The first log term adds the gain from amplifier power above 1 watt; the second subtracts the inverse-square distance loss of 6 decibels per doubling. The result assumes a point source in free field.
Why does doubling power add only 3 decibels?
Decibels of level are 10 times the base-10 logarithm of the power ratio. Doubling power gives 10 times log10(2), about 3.01 decibels. So to gain 10 decibels you need ten times the power, and to gain the same 6 decibels you get from halving distance, you need four times the power.
Does this include room gain or speaker placement?
No. This is the free-field estimate. Real rooms add reverberant energy and boundary reinforcement (placing a speaker against a wall or in a corner raises low-frequency output), and directivity varies with angle. Use this as the on-axis free-field baseline.
Official sources
- International Organization for Standardization: ISO 9613-1 sound propagation.
- U.S. National Institute of Standards and Technology: nist.gov.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.