Instructions
List all of the reactants that are going to be in your fission reaction. The reactants are everything that you have at the start of the reaction. This includes the atom that is going to split into two, as well as any other particles. While some atoms are naturally unstable, and likely to split into two on their own, often an additional particle is needed to excite them to a state where fission is likely.
List all of the products of your reaction. The products will likely be two smaller similar (or identical) atoms roughly half the size of the atom being split, as well as possibly some emitted particles.
Write down the mass of each of the particles and atoms on both sides of the equation. The mass will generally be represented in atomic mass units. If you examine the numbers, the amount of mass in the reactants will be greater than the amount of mass in the products. That extra mass is turned into energy. Take the difference between the mass of the products and the mass of the reactants.
Once you have the difference between the masses, multiply this number by 931.5. This is because there are 931.5 Mega Electron Volts, or MeV, per atomic mass unit. This gives an energy in the MeV, which can easily be converted into other standard energy units.