The formula for calculating energy is pretty simple. All you need is the bullet weight and muzzle velocity. It is:
Velocity X Velocity X Wt of the bullet in grains / 450240
For example a 230 gr bullet at 850 FPS.
850 X 850 X 230 / 450240 = 369 FT LBS energy.
...or just switch to the metric system (j)
velocity x velocity (m/s) x weight (kg, 1g = 0,001kg) / 2 = Energy (j)