Energy, TKO, OGW and IPSC PF

Energy
Energy, or more correctly, the Kinetic Energy, is calculated from the bullets weight and velocity.

TKO
Taylor Knockout Formula, as it misleading stands for, calculates a “knockout” factor based upon the velocity, bullet weight and caliber. The TKO formula favors larger calibers with heavy bullets, rather then small bore and high velocity calibers. When used on conventional rifle calibers, the TKO formula will give you a value for comparing different calibers and loads.

OGW
The OGW is an abbreviation for Optimal Game Weight formula. Compared to the TKO formula, this will give more credit to faster bullets, but will also favor heavier bullets. The OGW result indicates the maximum animal weight this caliber and load would effectively kill.

IPSC PF
This IPSC Power Factor is an index that tells us if the momentum is bellow or above the Minor/Major class limit.
The Minor class is for rounds with a PF larger then 150 and below 320.
The Major class is for rounds with a PF larger then 320.

Keep in mind that these formulas is a rather simple way of giving different loads and calibers a comparing index, not an exact value for how effective it is against a specific animal. Shot placement, bullet quality and distance (remaining speed of the bullet) are also essential criteria that will affect the “killing power” of a bullet.