The difference between the two spring height figures is 2.44 inches, which yields a product of 1,220 when multiplied by the spring rate of 500 lb/in. This spring needs to reach a solid height of 3 inches, therefore having to travel 2 inches. Well – going back to your rate of pay, if you make \$10 per hour and only work for 15 minutes, don’t you want to make \$2.50? To calculate the working load of how much force you’ll need in order to reach a solid height of 3 inches, you’ll have to multiply the distance traveled by the spring rate as shown in the following formula and diagram. Definition: Spring rate, also known as spring constant, is the constant amount of force or spring rate of force it takes an extension or compression spring to travel an inch of distance or, in the metric system of measurement, a millimeter of distance.The units of measurement of rate in the English System are, lbf/in (pounds of force per inch) or N/mm (newtons per millimeter) in the Metric System. Linear vs. ProgressiveA linear spring has the same spring rate throughout its compression range. I’m Low Spring Rates. Progressive-rate springs have a variable spring rate that increases as the spring is compressed. The constant of a whole spring is force per unit length of extension the rate constant will be F/L/L so force.