Factor Of Safety Calculator

Work out factor of safety instantly with clear inputs, formula shown and shareable results.

About Factor Of Safety Calculator

The factor of safety is material strength divided by working stress, so 250 MPa yield against 100 MPa working gives 2.5. It absorbs uncertainty in loads, material variation and analysis error rather than representing spare capacity to be used. Typical values run 1.5-2 for aircraft where weight is critical and 4-8 for lifting gear.

Formulas

Factor of safety

FoS = material strength / working stress

Margin of safety

margin = (FoS - 1) x 100%

Worked example

With the default values below, Factor Of Safety Calculator returns Factor Of Safety of 2.500. Change any input above and every figure here is recalculated in your browser.

Inputs used

Material strengthminimum 0 MPa: 250 MPa
Actual working stressminimum 0 MPa: 100 MPa

Results

Factor Of Safety: 2.500
Margin Of Safety: 150.00%
Stress Headroom Left: 150.00 MPa
Assessment: Conventional design range

Step by step

1Values used
2Factor of safety
3Margin of safety
4Factor Of Safety= 2.500
5Margin Of Safety= 150.00
6Stress Headroom Left= 150.00 MPa
7Assessment= Conventional design range

Assumptions and limits

The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Should I use yield or ultimate strength?

Yield for ductile materials in service, since permanent deformation is already failure. Ultimate is used for brittle materials and for collapse checks.

Is a high factor always better?

No. It costs weight, material and money, and an over-heavy part can push loads elsewhere. Codes specify the appropriate value.