Found this generator at Home Depot. "deal of the day"

While a 3db increase is a doubling of power, it is not a doubling of loudness. Loudness is subjective since the human ear is being used as a measuring device. If you take a couple of hundred people and ask them to turn up a sound source until it is twice as loud, the average change would be around 10db. A trained ear can hear a 1db level difference, however most individuals require a larger increase to detect a change unless listening to a single frequency tone.

As 12thgenusa noted, Decibels are logarithmic. It takes some adjustment of logic to accept that a 3db change is doubling, a 10db change is 10X power, 20db change is 100X power, a 60db change is 1,000,000X power, etc.