Amplifier (dB calculation)

There are two important dB calculation for amplifier output. 

1. How many dB SPL between two wattage levels.
2. The difference in watts that need to be achieved for a given change in dB SPL.

WATTS TO dB ( Watts to SPL):
You want to change a 100W amplifier to 350W amplifier. How many more dB you can get out of your loudspeaker?
Answer : dB = 10 x log ( watts 2 / watts 1) or 10 log ( 350/100) = 5.4 dB