Watts to Decibels
Estimate loudspeaker output in decibels from power and sensitivity.
About Watts to Decibels
Every tenfold increase in power adds ten decibels, while doubling the distance removes six decibels at the listening spot. Matching amplifier power to the level you need in a room avoids either wasting watts or driving speakers into distortion.
Formula
Watts to Decibels
SPL = sensitivity + 10 x log10(watts) - 20 x log10(distance)
- sensitivity
- SPL a speaker produces at one watt measured one metre away
Worked example
With the default values below, Watts to Decibels returns Output at Distance of 101.0. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Sensitivityaccepts 60–120 dB
- 87 dB
- Amplifier powerminimum 0.01 W
- 100 W
- Listening distanceminimum 0.01 m
- 2 m
Results
- Output at Distance
- 101.0 dB
- Output at 1 m
- 107.0 dB
- Distance Loss
- 6.0 dB
Step by step
- 1Values used
- 2Watts to Decibels
- 3Output at Distance= 101.0 dB
- 4Output at 1 m= 107.0 dB
- 5Distance Loss= 6.0 dB
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Watts to Decibels calculated?
SPL = sensitivity + 10 x log10(watts) - 20 x log10(distance) Every tenfold increase in power adds ten decibels, while doubling the distance removes six decibels at the listening spot.
Why does Watts to Decibels matter?
Matching amplifier power to the level you need in a room avoids either wasting watts or driving speakers into distortion.
What values do I need to enter?
This calculator takes 3 inputs: Sensitivity, Amplifier power, Listening distance. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.