Factor of Safety Calculator
Compare a stated material strength with applied stress and a user-selected target factor, including allowable stress and scalar margin.
Calculate a scalar strength-to-stress factor for a specified material failure mode. A separate target factor lets you see the corresponding allowable stress, utilization and margin without assuming that one default target applies to every structure.
How to use this tool
- Choose yield, ultimate or another stated strength basis.
- Enter positive strength and applied stress magnitudes, selecting their units independently.
- Enter the target factor required by your chosen assessment.
- Read the scalar margin alongside the assumptions behind the supplied strength and stress.
Formula
factor = strength / applied stress; allowable = strength / target; margin = factor / target − 1
Utilization is applied stress divided by the target allowable stress, expressed as a percentage. A margin of zero means equality with this scalar target, and a negative margin means it is exceeded. Strength and applied stress must describe the same failure mode and compatible material conditions.
Example
For 250 MPa strength, 100 MPa applied stress and a target factor of 2, the strength-to-stress factor is 2.5. Allowable stress is 125 MPa, utilization is 80%, and margin relative to the target is 0.25.
Frequently asked questions
Is the target factor automatically selected from a code?
No. The target is an input assumption. Applicable factors depend on the design basis, failure mode, loading, evidence and governing requirements.
Can I combine tensile and shear stress here?
Not by simply adding them. Combined loading needs an appropriate failure criterion and compatible strengths. This tool evaluates one supplied scalar stress and strength pair.
Why is zero applied stress rejected?
It makes the strength-to-stress ratio unbounded rather than a finite factor. Zero nominal stress also does not assess other loads, fatigue, buckling or defects.
Sources
Last updated: 2026-10-30