Like particles of matter and antimatter react to form energy in a 100% efficient reaction. Therefore, as an example:
electron (e[sup]-[/sup]) + positron (e[sup]+[/sup]) ----> energy.
You can use the famous E=mc[sup]2[/sup] equation to figure the total energy released.
Mass of e[sup]-[/sup] = 9.11 × 10[sup]-31[/sup] kg
Mass of e[sup]+[/sup] = 9.11 × 10[sup]-31[/sup] kg
And c = 300,000,000 m/s (speed of light)
Now this is not entirely accurate as this is a calculated rest mass for electrons. Particle mass in physics is measured in eV or electron volts because this takes into account its motion but for this example we'll use rest kilogram estimate so that the results will be something familiar to everyone.
E = (9.11 × 10[sup]-31[/sup] kg + 9.11 × 10[sup]-31[/sup] kg)(3 x 10[sup]8[/sup])[sup]2[/sup]
E = (1.822 x 10[sup]-30[/sup]) (9 x 10[sup]16[/sup])
E = 1.64 x 10[sup]-13[/sup] Joules for a single electron/positron annihilation
Doesn't seem like much but what if you had 1 kilo total matter/antimatter
E = (1 kg)(9 x 10[sup]16[/sup])
E = 9 x 10[sup]16[/sup] Joules or 90,000,000,000,000,000 Joules
Whoops I was an order of magnitude off on the example of destruction I just posted so here is the corrected energy equivalent: 21.5 megatons of TNT.