Safety factor terminology

When discussing safety factors, the following terms are often used:

• Design Factor: This is the minimum allowable safety factor that a design should achieve. It is a value dictated by the appropriate codes, design standards, and acceptable practices. It is not to be confused with the actual resultant safety factor of a design (next bullet).
• Safety Factor (or Factor of Safety): This is the actual resultant safety factor calculated from the stress results and material yield or ultimate tensile strength (as previously defined on this page).
• Margin of Safety: This quantity is a measure of the excess capacity of a part or structure. If the part is subjected to the greatest expected loading scenario, the Margin of Safety indicates how many more loads of the same magnitude the part can withstand before failing. Simply stated, Margin of Safety = Safety Factor – 1. For example, if a part has a safety factor of 2.5, the margin of safety is 1.5 (2.5 - 1), meaning that one and a half times the applied load can be added to the applied load before failure begins to occur.