The calculator will calculate the load on the sling. Simple and easy to use. Take the guess work out of how much force is exerted on a sling when making a lift with two or more lifting straps. The angles are not always just 45 or 60 degrees as is often listed on the sling capacity tag. Here is an easy way to figure out if it will be a safe lift. All you need to know are four things: 1. The rated vertical safe working load of the sling. 2. The total weight of the load. 3. The length of the sling from the hook to the attachment point. 4. The vertical distance from the load to the hook point.