Factor of Safety Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
Enter Values
How to use this calculator
- Enter the material strength (yield or ultimate stress) in MPa.
- Enter the applied (working) stress in the same units.
- Read the factor of safety and the stress margin.
How it works
The Factor of Safety Calculator divides the strength a part can take by the stress actually applied: FoS = strength ÷ applied stress.
A value above 1 means there's reserve capacity; below 1 the part is overstressed. The margin shows how much head-room you have as a percentage.
Worked example
250 MPa yield, 100 MPa applied. FoS = 250 / 100 = 2.5 — the part carries 2.5× the working stress before reaching yield (150% margin).
Tips
- Compare the applied stress from the Bending Stress or Stress & Strain calculators.
Frequently asked questions
What factor of safety should I use?
It depends on the code, the loading certainty and the consequences of failure — commonly 1.5–2 for well-understood static loads up to 4+ for shock loads, brittle materials or life-safety items. Always follow the governing standard.
Yield or ultimate strength?
Use yield strength if you must avoid permanent deformation, ultimate strength if you're guarding against fracture. Be clear which one your applied stress and target factor relate to.
Can I use these results for final design?
No. These calculators are for first-pass sizing, checking and learning. They assume ideal supports, static loads and elastic behaviour, and they don't apply load factors, member capacity, buckling or connection checks. Always verify against the relevant design code (e.g. AS 4100, AS 1170, Eurocode) and have a qualified engineer sign off structural work.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.