Amplifier power calculator
Flagship amplifiers advertise hundreds of watts per channel. Whether you need them depends on two numbers: how loud your speakers play from one watt and how far away you sit. This calculator gives the power each speaker needs to reach the peak levels used for home theater calibration, and what your amplifier can deliver.
Results are estimates for planning. Check the manufacturer's manual before you drill, buy or mount anything.
How it works
Sound level at the seat follows the speaker's sensitivity, the power and the inverse-square law:
SPL = sensitivity (1 W / 1 m) + 10 × log10(watts) − 20 × log10(distance in m)
Solving for power: watts = 10(target − sensitivity + 20 log10 d) / 10. Each doubling of power adds 3 dB; each doubling of distance loses 6 dB.
Targets: Dolby's home guidelines calibrate each speaker to 79–82 dB SPL with pink noise at −20 dBFS, depending on room size, so full-scale peaks reach 99–102 dB. Cinema reference is 85 dB at −20 dBFS, or 105 dB peaks. A sensitivity quoted at 2.83 V equals 1 W only into 8 ohms; into 4 ohms it is 2 W, so we subtract 3 dB.
Assumptions and limits
- It ignores room gain, which usually adds a few dB at the seat, and the boost from several speakers playing together. Both make the result conservative.
- Speakers compress at high power, and many amplifiers deliver less per channel with all channels driven. Leave margin for both.
- Subwoofers are calibrated and powered separately.
Sources
- Dolby Atmos Home Theater Installation Guidelines, calibration levels (Dolby, PDF)
- Inverse-square law (Wikipedia)
Last reviewed: November 2026.