Sound power level or acoustic power level is a logarithmic measure of the sound power in comparison to the reference level of 0 dB (decibels).

The measure of a ratio of two sound powers is

where W₁ and W₀ are the powers.

The sound power level is given the letter "L_w" or SWL and is measured in "dBW". dB is dimensionless.

If W₀ is the standard reference sound power, where

W₀ = 10 ^{- 12}W

(W = watt), then instead of "dB" we use "dB SWL". (SWL = sound power level).