where is a proportionality constant, is the cross-sectional area of the plunger, is the number of turns in the solenoid, is the current through the solenoid wire, and is the length of the solenoid. For units using inches, pounds force, and amperes with long, slender, solenoids, the value of is around 0.009 to 0.010 psi (maximum pull pounds per square inch of plunger cross-sectional area). For example, a 12-inch long coil () with a long plunger of 1-square inch cross section () and 11,200 ampere-turns () had a maximum pull of 8.75 pounds (corresponding to ).