Determine the mass of the object you want to move by weighing it on a scale. Multiply it by 9.8 -- gravitation acceleration on Earth -- to get the weight in newtons that it exerts. For example, suppose you have an object that has a mass of 20 kilograms. It weighs 196 newtons.
Find the length of the load arm in meters by measuring from fulcrum to the object's end of the lever. Multiply the length measurement by the object's weight to determine the load force. If you have a lever arm length of 2 meters, the total load force is 392 newtons.
Divide this by the amount of effort force exerted. If this comes from an object, weigh the object. For example, assume you have an object that weighs 30 newtons. 392 divided by 30 is 13.066. Therefore, you need an effort length of 13.066 meters to apply enough force to lift the object.