Store-bought log splitters are listed with specs, including splitting force, which is usually expressed in pounds or tons. The higher the splitter's pressure rating and piston area, the higher the splitting force will be. Because log splitters use hydraulic systems, you need to use the force of a hydraulic cylinder equation.
Measure the diameter of the piston. As an example, a piston has a diameter of 5 inches.
Square the diameter, multiply it by 3.14 and divide the result by 4 to calculate the area of the piston. In the example, squaring the diameter of the piston gives you 25, multiply 25 by 3.14 gives you 78.5 and dividing 78.5 by 4 gives you 19.625 inches squared.
Multiply the piston's area by the splitter's pressure rating. In the example, the splitter has a pressure rating of 3,000 pounds per square inch (PSI). Multiplying 19.625 by 3,000 gives you 58,875. The log splitter has a splitting force of 58,875 lbs..