Margin of safety (measure of requirement verification)


Many government agencies and industries (such as aerospace) require the use of a margin of safety (MoS or M.S.) to describe the ratio of the strength of the structure to the requirements. There are two separate definitions for the margin of safety so care is needed to determine which is being used for a given application. One usage is as a measure of satisfying design requirements (requirement verification). 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. 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)
RFSRealized factory of Safety (dimensionless)
DSFDesign Safety factor (dimensionless)