The amount of force required to break a human bone varies depending on which bone and its density. On average, the human femur requires 1,700 pounds per square inch to be cleanly broken, while a weaker bone, such as the clavicle, takes considerably less force to break.
Many factors influence how easily a bone is broken. The density of the bone and the force being put on it must both be calculated. If the force is concentrated to a single point, it is easier to break a bone. A bone with higher density requires a higher amount of PSI to break.