Isoton
An isoton was a measure of both mass and explosive yield used by at least Federation, Dominion, Borg, and Malon science during the 24th century and Kyrian in the 31st century.

Comparative list of measure

As a measurement of mass
Isogram = 1 one-millionth of an isoton
 A few isograms of dilithium crystal was barely enough to power the sonic showers of a starship. ()
10 isograms of antimatter-eminating ular matter from the body of a nucleogenic lifeform were sufficient to enhance the 's warp factor by .03 percent for one month. ()

Isoton
 10 isotons of explosives were ordered by Kilana to be fired by her Jem'Hadar troops near a Jem'Hadar attack ship in which a team from Deep Space 9 was seeking shelter in 2373. ()
 12 isotons of zeolitic ore was proposed by Captain Kathryn Janeway for trade with the Annari in exchange for deuterium injectors in 2377. ()
 90 million isotons of antimatter waste could be transported by a Malon export vessel, eleventh gradient. ()
 6 billion isotons of antimatter waste was produced daily, in 2375, by the Malon civilization as an industrial byproduct. ()
 4 trillion isotons of antimatter waste could be transported with another type of Malon export vessel. ()

As a measurement of energy 
Isoton
 A 25 isoton photon torpedo explosion could destroy an entire city within seconds. ()
 A 54 isoton yield gravimetric charge could blow up a small planet. ()
 An 80 isoton yield gravimetric torpedo was used by  to destroy a harmonic resonance chamber containing approximately 144 million omega molecules (72% of approximately 200 million) in 2374. ()
 A 90 isoton bomb of enriched ultritium had the explosion  of 800 kilometers. Such a bomb was used to blow up a ketracel-white facility in Cardassian space in 2374. ()
 200 isotons was the explosive yield of a Photon torpedo with a class-6 Warhead. ()
 320 isotons was the explosive yield of a Class 12, Mark VI long-range photon torpedo. (, display graphics)
 A 5 million isoton explosion of a multi-kinetic neutronic mine could affect an entire star system. The shock wave had a dispersive force radius of five light years. ()

Appendices

Background information 
The  credited Andre Bormanis with the invention of this term. The authors of this reference work stated that this term might never be defined precisely.

According to the Star Trek: Deep Space Nine Technical Manual, 25 isotons is the maximum theoretical yield of a matter-antimatter reaction in photon torpedoes and that quantum torpedoes have at least twice the yield at 52.3 isotons. (p. 85) These figures are not compatible with the canonical statements in  of 200 isotons as the yield of a class-6 photon torpedo warhead and in  of 320 isotons as the yield of a class-12 photon torpedo. As with most other measures used in Star Trek there are no direct conversions to real world measures given. 

In the Star Trek: The Next Generation Technical Manual a figure of 1.5 kg of antimatter is given as the amount of warhead material carried by a standard photon torpedo. (p. 129) Using standard physics calculations a direct 1:1 detonation would generate a energy equivalent of 64.4 megatons TNT. Warhead materials are however premixed to achieves the level of destructive force of an antimatter pod rupture containing 100 cubic meters of antideuterium. (p. 69) Antimatter is stored as liquid or slush on starships. (p. 68) Density of mere liquid antideuterium is around 160 kg per cubic meter. According to this comparison the destructive effect in the high annihilation rate energy release would be comparable to the effects of a 690 gigaton blast. Furthermore it is not clear if the 1.5 kg should be compared to the 200 - 320 isoton figures given on screen later on, or the 25 isoton figure given in the Star Trek: Deep Space Nine Technical Manual reference book to make a conversion.

External link 
 

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Measurements