Working load (WL) is the load that a rope is subjected to during normal use. WLs are based on a percentage of the breaking strength (aka tensile strength) of new and unused rope. They are calculated by dividing the rope’s breaking strength (BS) by a safety factor (SF). The breaking strength of Amsteel Blue 7/64 is 1600 pounds. Samson recommends that the maximum workload should be 1/5th, or 20% of the quoted breaking strength (safety factor = 5), and recommends a higher safety factor for uses that involve “life or limb.” The Cordage Institute recommends safety factors of 5 to 12 for non-critical uses, and 15 for lifelines. Here is the weight that a typical 7/64 Amsteel Blue whoopie sling is rated to support, using the minimum safety factor recommended by Samson: SWL = BS / SF = 1600 / 5 = 320 lbs. Note: I had originally posted a calculation based on plain Amsteel, which gave rise to some of the responses below. Don’t get confused.