Factor of Safety Calculator
Calculate factor of safety from strength and stress.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Request a ToolHow to Use the Factor of Safety Calculator
Enter material strength and actual stress.
- Enter strength. Yield or ultimate strength depending on criteria.
- Enter stress. The calculated or expected stress.
- Read the result. FOS greater than 1 means the design is safe.
About the Factor of Safety Calculator
The factor of safety (FOS) is the ratio of a material's strength to the actual or expected stress. An FOS of 2 means the part can withstand twice the design load before failure. Typical FOS values range from 1.5 for well-understood loads to 10 for uncertain or safety-critical applications. Building codes specify minimum FOS values for various structural elements.
Frequently Asked Questions
What factor of safety should I use?
It depends on the application. Typical values: 1.5-2 for well-understood static loads, 2-3 for dynamic loads, 3-4 for structures with uncertain loads, and higher for safety-critical applications.
What if FOS is less than 1?
An FOS below 1 means the stress exceeds the material strength and the part will fail. The design must be revised immediately.
Should I use yield or ultimate strength?
Use yield strength for designs that must not permanently deform. Use ultimate strength for designs where some deformation is acceptable but fracture must be prevented.