This is a direct quote from kindasf on reddit because I'd like to give him the credit; "Let's say you have a 10 ton cylinder with a 1.5 inch diameter ram that has an operating ceiling of 10,000 PSI. That means that if the hydraulic fluid between the pump and the cylinder is at 10,000 PSI, the force across the 1.5 inch ram is 10 tons, or 20,000 lbs. Let's say you also have a 4x4 prepress mold, that's 16 square inches. Now that we know those things, we can convert the force at the cylinder to PSI at the material. First we divide the cylinder circumference area by the material area to get a ratio. A circles area is Pi x Radius squared. Solve for 1.5 diameter, and you have 1.77 square inches of surface area. 16 square inches of material / 1.77 square inches of cylinder head area = 9.039 So now we can use that ratio to divide the force. 20,000 lbs of force / 9.039 = 2212 pounds of pressure at the material. Divide that by 16 square inches and you have 138 PSI at the material. This is a good example of why a narrow cylinder at 10 tons is not enough pressure for a 4x4 pack. Don't forget that you really don't want to push hydraulics past 75% if you want them to last."