Margin of safety for failure load (measure of requirement verification)


Many agencies and organizations (such as aerospace) define the margin of safety (MoS or M.S.) including the design factor, in other words, the margin of safety is calculated after applying the design factor. In the case of a margin of 0, the part is at exactly the required strength (the safety factor would equal the design factor). If there is a part with a required design factor of 3 and a margin of 1, the part would have a safety factor of 6 (capable of supporting two loads equal to its design factor of 3, supporting six times the design load before failure). A margin of 0 would mean the part would pass with a safety factor of 3. If the margin is less than 0 in this definition, although the part will not necessarily fail, the design requirement has not been met. A convenience of this usage is that for all applications, a margin of 0 or higher is passing, one does not need to know application details or compare against requirements, just glancing at the margin calculation tells whether the design passes or not. This is helpful for oversight and reviewing on projects with various integrated components, as different components may have various design factors involved and the margin calculation helps prevent confusion. For a successful design, the Realized Safety Factor must always equal or exceed the Design Safety Factor so the Margin of Safety is greater than or equal to zero.

The Margin of Safety is sometimes, but infrequently, used as a percentage, i.e., a 0.50 M.S is equivalent to a 50% M.S. When a design satisfies this test it is said to have a “positive margin,” and, conversely, a “negative margin” when it does not.

Related formulas


MSmargine of safety (dimensionless)
FLfailure load (dimensionless)
DLdesign load (dimensionless)
DSFdesign safety factor (dimensionless)