What are the yield of fire power compared to conventional weapons?

I seen 3 photon torps in "ent" take out the inside of a one story building. I have also seen 3 quondam torp in "Movie" take out a borg sphere.

Which suggests photon torps may be the strength of a artillery round.

quondam may be the strength of of a 3 tun bomb.

check out "Storm Front" Part 8 skip to 06:20 on the time bar. YouTube - "Storm Front" Part 8

The torp dose not nook like a nook at all. Nooks start with a flash then the mushroom cloud shows its ugly head.

Heres usas nuke test looks nothing like in ent.

YouTube - Nuke Test 2

It did not look like that much power is what I was trying to say in the clip. and when the borg used there granitic torps in 1st contact they jut took out one building at a same and some time not even the building was distorted.

What about the gravimetric topedos in the movie 1st contact?

I think we're severely underestimating the power of antimatter annihilation relative to nuclear fission and fusion. In fisson or fusion, a tiny percentage of the available mass is converted in to energy (the mass defect). Even a small amount of mass results in the release of an inconceivable amount of energy; this is simply because to calculate the energy released, we multiply the mass loss by the square of the speed of light.

Does everyone realise that in an antimatter reaction, all of the mass, both matter and antimatter, is converted to photons? If the warhead in a photon torpedo had the same mass as that in a nuke, it would result in a shockingly huge detonation, and would make a nuclear explosion look feeble by comparison. Presumably the detonation is controlled by making the warhead tiny.

But there is one problem in star trek battles: the warp engine, which controls an antimatter reaction big enough to warp space. A warp core breach would be orders of magnitude bigger than that depicted in the show. Not only that, but a warp core breach would occur everytime a ship is destroyed (you cannot keep the matter and antimatter separate once the antimatter confinement fails). The resulting detonation would wipe out an entire fleet of starhips, ending the battle quickly. And would probably take the nearest solar system along with it.

Just my "two cents". 

i thought quantum torps used quantum shielding to direct the full force of the antimatter detonation towards the target or it's shields, like a shaped charge. photon torps waste 75% of it's energy because most of the explosion is directed outwards, where as a quantum torp will hit it's target with roughly 80% of it's total energy output. so a quantum torp is about 3 time as powerful as a standard photon torp.

or am i wrong?

The writers are just using some licence when they think up things like quantum shields, they really don't know what that is, and they're probably unconcerned.

Needless to say, if we were ever capable of creating an antimatter weapon, we'd never need to upgrade it using hard to access zero point energy. We'd just have to use a bigger warhead. A few more nanograms.

Thanks for the calculation Mortographer, I didn't think it was necessary but numbers can help us to appreciate the scale. I'd like to point out that possibly you meant Joules rather than Jewels, and grams rather than grammes?  Sorry to be an arse.

Btw zero point energy is only a theory in the sense that gravity is a theory - it is very real. You can use schrodinger's equation to calculate vibrational energy levels, and the ground state has non-zero energy. Therefore a system at zero Kelvin will have residual energy. Whether you can access it, that's another matter.