What is factor of safety (FoS)?

FoS is the ratio of material strength to the actual applied stress. A FoS above 1 indicates the design can carry the load under the assumed conditions.

Should I use yield or ultimate strength?

Use yield strength (Sy) for ductile materials when permanent deformation is the limiting state. Use ultimate strength (Su) for brittle materials or when fracture is the limiting state.

Is factor of safety unitless?

Yes. FoS is a ratio of two stresses (strength and applied stress), so units cancel out.

What is margin of safety (MS)?

Margin of Safety is MS = FoS − 1. A positive MS indicates additional capacity beyond the working load.

What are typical target FoS values?

Typical targets vary by industry and uncertainty. For well-controlled, tested components FoS can be 1.2–1.5; for common mechanical designs 1.5–2.0; for high uncertainty or life-safety systems, higher values may be mandated by codes or standards.

How does stress concentration affect FoS?

Applied stress should include local peak stresses (e.g., Kt effects). Using a lower, averaged stress can overestimate FoS.

What happens if applied stress is zero?

FoS tends to infinity mathematically. In practice, verify that your loading and stress computation are correct.

Factor of Safety Calculator

Professional factor of safety (FoS) calculator for mechanical engineers. Compute FoS, margin of safety, and allowable stress from material strength and applied stress. WCAG 2.1 AA accessible, mobile-first, and optimized for Core Web Vitals.

Full original guide (expanded)

Audit: Complete

Formula (LaTeX) + variables + units

This section shows the formulas used by the calculator engine, plus variable definitions and units.

Formula (extracted LaTeX)

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Formula (extracted text)

FoS = Strength / AppliedStress MS = FoS - 1 σ_allow = Strength / FoS_target σ = F / A Select strength as Sy (yield) for ductile design or Su (ultimate) for brittle/fracture-limited design.

Variables and units

No variables provided in audit spec.

Sources (authoritative):

Official NASA standard — standards.nasa.gov · Accessed 2026-01-19
https://standards.nasa.gov/standard/nasa/nasa-std-5001
Engineering — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/engineering
Publisher page — mheducation.com · Accessed 2026-01-19
https://www.mheducation.com/highered/product/shigley-s-mechanical-engineering-design-budynas-nisbett/M9781260367051.html

Changelog

Version: 0.1.0-draft
Last code update: 2026-01-19

0.1.0-draft · 2026-01-19

Initial audit spec draft generated from HTML extraction (review required).
Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
Confirm sources are authoritative and relevant to the calculator methodology.

Verified by Ugo Candido on 2026-01-19
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, ', svg: { fontCache: 'global' } };

Audit: Complete

Formula (LaTeX) + variables + units

This section shows the formulas used by the calculator engine, plus variable definitions and units.

Formula (extracted LaTeX)

\[','\]

','

Formula (extracted text)

FoS = Strength / AppliedStress MS = FoS - 1 σ_allow = Strength / FoS_target σ = F / A Select strength as Sy (yield) for ductile design or Su (ultimate) for brittle/fracture-limited design.

Variables and units

No variables provided in audit spec.

Sources (authoritative):

Official NASA standard — standards.nasa.gov · Accessed 2026-01-19
https://standards.nasa.gov/standard/nasa/nasa-std-5001
Engineering — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/engineering
Publisher page — mheducation.com · Accessed 2026-01-19
https://www.mheducation.com/highered/product/shigley-s-mechanical-engineering-design-budynas-nisbett/M9781260367051.html

Changelog

Version: 0.1.0-draft
Last code update: 2026-01-19

0.1.0-draft · 2026-01-19

Initial audit spec draft generated from HTML extraction (review required).
Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
Confirm sources are authoritative and relevant to the calculator methodology.

Verified by Ugo Candido on 2026-01-19
Profile · LinkedIn

]], displayMath: [['\\[','\\]']] }, svg: { fontCache: 'global' } };, svg: { fontCache: 'global' } };

Audit: Complete

Formula (LaTeX) + variables + units

This section shows the formulas used by the calculator engine, plus variable definitions and units.

Formula (extracted LaTeX)

\[','\]

','

Formula (extracted text)

FoS = Strength / AppliedStress MS = FoS - 1 σ_allow = Strength / FoS_target σ = F / A Select strength as Sy (yield) for ductile design or Su (ultimate) for brittle/fracture-limited design.

Variables and units

No variables provided in audit spec.

Sources (authoritative):

Official NASA standard — standards.nasa.gov · Accessed 2026-01-19
https://standards.nasa.gov/standard/nasa/nasa-std-5001
Engineering — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/engineering
Publisher page — mheducation.com · Accessed 2026-01-19
https://www.mheducation.com/highered/product/shigley-s-mechanical-engineering-design-budynas-nisbett/M9781260367051.html

Changelog

Version: 0.1.0-draft
Last code update: 2026-01-19

0.1.0-draft · 2026-01-19

Initial audit spec draft generated from HTML extraction (review required).
Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
Confirm sources are authoritative and relevant to the calculator methodology.

Verified by Ugo Candido on 2026-01-19
Profile · LinkedIn

Formulas

(Formulas preserved from original page content, if present.)

Version 0.1.0-draft

Citations

Add authoritative sources relevant to this calculator (standards bodies, manuals, official docs).

Changelog

0.1.0-draft — 2026-01-19: Initial draft (review required).