Star Trek is extremely inconsistent with yields. A gravimetric torpedo was said to have a yield of 80 isotons, even though it was said that a 54 isoton gravametic torpedo was enough to destroy a small moon. Gravimetric torpedoes are implied to be a lot more powerful than a photon torpedoes. Yet in VOY: Scorpian Part 2, a class-6 photo torpedo was said to have a yield of 200 isotons. Also in Star Trek Into Darkness the class-12 photon torpedoes are said have a yield of 320 isotons. But neither of these torpedoes are clearly powerful enough to "destroy a small moon". The technical manuals states that the gravametric torpedoes are highly destructive and an 80 isoton gravametric blast is far more powerful than an 80 isoton antimatter blast.
According to the the Kyrian curator Quarren, Voyager's photon torpedoes were said to have a 25 isoton yield, which could destroy an entire city within seconds, but the Kyrian got a lot of details about Voyager very wrong, so this may be in error.
Also over the course of VOY, the ship was said to have several different classes of torpedo (e.g. class 7 or class 9) in it's arsenal, which seemed to be differentiated by maximum yield. Furthermore throughout Star Trek it is stated that torpedoes have a variable yields anyway.
The TNG and DS9 technical manuals give differing figures. The TNG:TM said a photon torpedo was good for a 690 gigaton explosion, which is about 69% of the combined destructive force of every nuclear weapon in existence today.
The DS9:TM states that the Mark XXV torpedo was the current design as of 2375. It has a dry mass of 186.7 kilograms (which would create an 800 gigaton explosion in the real world), leading to a yield of 18.5 isotons. It is specifically stated to be 5% more powerful than the Mark XXIV. The DS9:TM also stated that a maximum yield a photon torpedo can attain is 25 isotons. While the Mark I quantums used later in DS9 and in the TNG movies are said in the DS9 technical manual of 50 isotons.
There is no real world conversiont for isotons. Sorry I couldn't be more helpful I suggest you simply use this information to make up your own mind, and maintain consistancey whenever you use it. Alooph Looq (talk) 17:03, August 28, 2013 (UTC)